Differential diagnosis refers to the process by which a clinically significant problem or set of symptoms is evaluated and distinguished from other conditions, usually associated with similar clinical features. In the case of mental retardation, many neurodevelopmental and psychiatric disorders can mimic or accompany the mental retardation diagnosis. These other disorders may also be independent grounds for Supplemental Security Income (SSI) and Disability Income (DI) benefits eligibility. It is often challenging for the Social Security Administration (SSA) disability determination specialist to distinguish between mental retardation and other neurodevelopmental and psychiatric disorders with similar signs and symptoms. In addition, when these other disorders are present in addition to mental retardation, they may make assessment of intellectual and adaptive functioning even more complicated than it frequently is. In such cases, it is imperative that clinical
evaluations take these complex factors into consideration and draw conclusions based on objective data and best clinical practice.
This chapter focuses on the challenges likely to be encountered in determining eligibility for SSI and DI benefits through a diagnosis of mental retardation. As outlined in earlier chapters, especially Chapter 2, the accuracy of the diagnosis of mental retardation is crucial both to SSA and to the client: to the former so that it can carry out its mandate, and to the latter for essential income support and as a gateway to other needed entitlements. While earlier chapters dealt with issues related to defining mental retardation and to the diagnostic criteria for this condition, here we consider distinguishing mental retardation from other conditions. In addition, we review circumstances that can complicate the process of assessment and discuss pertinent issues in evaluating intellectual and functional status across the life span.
The prevalence of mental retardation is highest among school-age populations (e.g., Kiely, 1987; Larson et al., 2001) and, by definition, its symptoms must be present before adulthood, though actual diagnosis may not take place until after schooling ends. Depending on their state of residence, between 5.2 and 11.5 percent of all children attending public schools are currently classified as having a disability (not necessarily mental retardation) of sufficient severity to receive special services (U.S. Department of Education, 1994, Table AA25). However, eligibility for special services in school does not necessarily confer eligibility for SSI benefits. Most individuals with a diagnosis of mental retardation who receive special education services become gainfully employed once they leave the school system. There is, however, an increased probability that individuals in this population may need financial support at some time during their adult lives.
Mental retardation is a prevalent disability among the population receiving special education services, but substantial numbers of these individuals will have some other condition associated with varying degrees of disability, including developmental, learning, sensory, motor, or psychiatric disability. These conditions produce a wide range of impairments, and to a greater or lesser degree can share signs or symp-
toms with mental retardation. It is important to determine the nature of each individual’s limitations in order to develop plans for education, habilitation, and vocational training, as well as for making SSI eligibility determinations.
CLINICAL CONSIDERATIONS AND ELIGIBILITY DETERMINATION
To arrive at a correct diagnosis or case classification, clinicians evaluate the client’s signs and symptoms and compare them to those of other similar conditions. Additional information is then gathered to rule out possibilities systematically until a valid diagnosis can be made. Symptoms refer to the concerns expressed by the affected individual or his or her representatives, while “signs” are objective findings from a physical examination, laboratory tests, psychological assessment, or educational evaluation.
In the case of mental retardation, presenting signs and symptoms are usually evident and associated with underlying intellectual and adaptive impairments. Nevertheless, differential diagnosis can be complicated by at least four other factors. First, the severity and nature of impairments can vary substantially, with each person having his or her own strengths and weaknesses in performance. Thus, clinical presentation may be different among affected individuals, some of whom have abilities that are only subtly different outside the classroom setting from those of people without mental retardation. Second, the specific manifestations of mental retardation change with development throughout the life span. In less severe cases, it is difficult to be confident about a diagnosis made during infancy or early childhood, yet assessment is rarely conducted for clients after they leave school. Third, other conditions can produce signs and symptoms very similar to those of mental retardation, especially before elementary school begins. These include other developmental, learning, sensory, and motor impairments. In adolescence or young adulthood, psychiatric impairments may become increasingly evident, further compli-
cating determinations of mental retardation or even exacerbating its effects. Finally, there are a number of other conditions that can complicate assessment and make it difficult to determine whether a diagnosis of mental retardation actually is an underestimation of a person’s true capabilities. These issues are all reviewed in this chapter, with particular attention to their significance in the context of eligibility for SSI and DI.
Eligibility for Support
It is sometimes difficult to distinguish between mental retardation and other conditions currently covered by SSI, the so-called categorical disorders: autism, learning disability, borderline intellectual functioning, and organic mental disorders marked by specific behavioral phenotypes. It is particularly important to make these distinctions when selecting treatments and developing plans for education, habilitation, and vocational training. Diagnostic information is used in making very different types of decisions in clinical, educational, vocational, and SSI contexts. In educational settings, it is critical to determine if a condition other than mental retardation (like a specific learning disability or sensory, motor, or psychiatric impairment) is causing or contributing to poor performance. These differential diagnoses have direct implications for developing individualized plans of treatment and instruction to encourage learning. In clinical settings, arriving at the correct differential diagnosis determines appropriate and effective treatment and prevention strategies.
In the SSI context, the explicit focus is on eligibility for support— that is, current employability for adults and marked or severe limitations in developmental skills for children. For SSI eligibility, the underlying cause or origin of intellectual or functional impairment is not important if the individual meets the income criteria and intellectual disability definitions for mental retardation. Eligibility is dependent on the severity of impairment regardless of its source. Therefore, the primary goal of a diagnosis differentiating between mental retardation
and some other condition is not relevant when the severity of disability clearly meets or exceeds eligibility criteria within SSA guidelines. This would include situations in which either the total IQ test score is less than 60 or the individual has another condition that is so disabling that it interferes with the determination of true intelligence, such as blindness, deafness, uncontrolled seizures, cerebral palsy, or some other disorder. Similarly, once eligibility for SSI benefits for individuals with mental retardation is determined, the decision process does not need to consider additional comorbid disorders, and the process of differential diagnosis need not continue further.
Differential diagnosis is a different matter for individuals having less severe disabilities that put them at the border of SSI eligibility criteria. For individuals with mild mental retardation, it is vitally important to generate a complete description of signs and symptoms, including diagnosis of comorbid conditions, as well as an accurate assessment of intellectual and functional status. Furthermore, the presence of additional disabilities in such cases can impair functioning to such an extent that competitive employment is unlikely or even impossible. For cases having less severe clinical presentations, carefully conducted evaluation procedures that include standardized assessments of intellectual development and adaptive function (see Chapters 3 and 4) can usually provide the accurate estimates of capabilities needed in arriving at a valid differential diagnosis, except perhaps for very young children.
Currently, SSA defines mental retardation by quantitative rather than qualitative performance criteria relative to age-referenced expectations. This is incorporated into SSA regulations, which include extended discussions of assessment methods and criteria that vary with age and with respect to broad domains of functioning. SSA has deliberately built some flexibility into its procedures for determining SSI eligibility at various chronological ages (Social Security Administration, 2000), but the clinician must recognize the strengths and limitations of assessment tools at each stage of development. Evaluators must be sensitive to the diagnostic precision of the instruments em-
ployed, aware of the types of errors that imprecision may introduce, and be able to access sources of additional information that can reduce the likelihood of misclassification. These issues are discussed at length in Chapters 2 and 3.
Individuals can qualify for SSI in two ways. The first and most obvious is by having a condition listed by the SSA as eligible by definition. Two lists define conditions that meet the standard for severity; one applies to both children and adults and the other list is for use with children under 18 years of age. These lists are intended to objectify and facilitate the determination process, but problems can arise because, as pointed out in earlier chapters, the clinical definitions of mental retardation provided in authoritative references (e.g., Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition—DSM-IV—American Psychiatric Association, 1994), are not the same as the criteria provided in the SSA listing. Because of this disparity, some individuals with a clinical diagnosis of mental retardation do not meet SSI eligibility criteria. SSI eligibility is intentionally limited to only those individuals whose disability is severe enough to impose substantial restrictions on their ability to work, either now or in the future.
Individuals can qualify for SSI support in a second way: they are eligible if their status is functionally equivalent to a listed condition. In the case of mental retardation, functional equivalence for children is assessed in six domains: (1) acquiring and using information, (2) attending and completing tasks, (3) interacting and relating with others, (4) moving about and manipulating objects, (5) caring for oneself, and (6) health and physical well-being (Social Security Administration, 2000). To meet functional equivalence criteria, the child must have either marked impairment (equal to or greater than 2 but less than 3 standard deviations below the mean on a standardized, norm-referenced assessment) in two domains, or extreme impairment (equal to or greater than 3 standard deviations below the mean) in a single domain. While this second path to eligibility offers children having unrecognized mental retardation an opportunity to obtain needed sup-
port, this opportunity rests to a substantial degree on the judgment of the examiner. Therefore, the use of uniform, valid procedures and criteria are essential for cases falling into this category, as well as for similar situations with adults.
Issues Associated with Life Span Development
Age-related considerations are crucial in making a diagnosis of mental retardation because key signs and symptoms, as well as appropriate assessment methods, are quite different across the life span. Abilities and socially appropriate expectations change dramatically with development, and these factors can complicate the evaluation process in distinct, age-specific ways. Because adaptive behavior changes and tends to increase with age (e.g., Hundert et al., 1997), most measures of adaptive behavior are structured so that items are presented in a developmental sequence. Declines in adaptive behavior can be associated with advanced aging, as it is in the general population, or at an earlier chronological age in the instance of some disorders, like Down syndrome (Kapell et al., 1998; Zigman et al., 1996), or in the presence of severe to profound mental retardation. Moreover, although there are systematic differences in the typical adaptive performance of people with mild mental retardation and their peers with more severe degrees of mental retardation, there is also overlap in adaptive behavior skills among people assessed with differing degrees of intellectual disability (Janicki & Jacobson, 1982). For example, it is possible for someone with mild mental retardation to have certain adaptive behavioral skills that are less advanced than those of another person with moderate mental retardation. These differences may reflect different experiences, opportunities, and participation in services. The following sections use four stages of maturation to identify and discuss key factors in making the differential diagnosis of mental retardation and determining SSI eligibility.
INFANTS, TODDLERS, AND PRESCHOOLERS
The limitations of current assessment technologies are a major problem in evaluating disability in very young children. Advances are being made rapidly, especially in identification of genetic conditions likely to increase risk, but diagnosis of mental retardation remains difficult except in cases with clear biomedical manifestations or severely delayed development. This is especially true until the age when language delays can be documented, or even later when academic achievement is regularly evaluated. For children under age 3, a developmental quotient (developmental age/chronological age × 100) may serve as a surrogate for standard IQ, such that quotients of less than 67 define marked impairment and quotients less than 50 define extreme impairment (Social Security Administration, 2000). This approach is currently considered to be the best available diagnostic practice, but it has limited predictive validity and precision. The distinction between generalized and specific delays, both of which can have an impact on function to a degree that will quality for SSI, often has to be postponed until later ages.
In preschoolers, language impairment is the most commonly identified specific developmental disorder. In principle, specific language impairment is distinguished from mental retardation by the relative preservation of nonlanguage skills. However, both conditions are frequently associated with social and behavioral deficits, and both are strong predictors of poor academic achievement at older ages (McArthur et al., 2000). Therefore, specific language impairment can be difficult to distinguish from mild mental retardation, as the following case illustrates.
Allen is a 3-year-old who has been referred for delayed language development. He was born at full term following an uncomplicated pregnancy. He is a healthy child whose early developmental milestones were achieved on time or only slightly delayed with the exception of language. He started speaking single words at 18 months of age, began using baby talk at 21 months and did not start speaking in phrases until recently. Allen waved “bye-bye” before his first birthday, knew some of his body
parts by 24 months, and follows some multistep commands. He likes to play and roughhouse with his 4-year-old brother. His hearing has been tested and found to be normal. His rate of language development has been approximately two-thirds of normal expectations. On formal evaluation he was found to be functioning in the low borderline range of intelligence but he showed clear unevenness in his results. Language abilities were in the deficient range, while problem solving abilities were in the borderline range. With this developmental profile, it is difficult to distinguish between specific language impairment or mild mental retardation. Early intervention should target development of language and general intellectual functioning, with frequent follow-up evaluations (at approximately six-month intervals) to monitor progress and refine diagnosis.
In Allen’s case, uncertainty regarding differential diagnosis can be resolved in a year or two when he can be given a detailed assessment that focuses on both language development and intelligence, but in many similar cases, diagnostic evaluations will be delayed until early in the child’s schooling.
In contrast to the severe constraints on the ability to diagnose mild mental retardation in young children, a great deal is now known about the conditions associated with increased risk for mental retardation. Babies born prematurely, very small for their gestational age, or exposed in utero to alcohol or other teratogenic agents are at increased risk of mental retardation. Babies are also at risk if their mothers are in their young teens, have a history of poor prenatal care, have less than a high school education, or are living in poverty (e.g., Sameroff, 1986). With particular relevance to SSI determination, many of these risk factors are also associated with economic disadvantage. However, while large numbers of young children are at risk, the majority of them do not have mental retardation. Current research is focusing on refining the ability to identify those children who will, in fact, develop atypically.
Accumulating evidence suggests that intervention may be most effective if it is initiated as early as possible, although there is still debate in the professional and scientific community on this point (Bailey et
al., 1999; Ramey & Ramey, 1999). Therefore, public health policy needs to weigh the relative value of providing earlier supports to an expanded subpopulation, only a subset of whom will prove to have a substantial disability, against the effect of delaying supports and treatments for a more limited number of individuals who may then need more intensive interventions over a longer period of time. A prime example of this dilemma has been highlighted in the field of autism, in which early, intensive treatment has produced a range of positive outcomes; for some children, the results of treatment have been dramatic (Lovaas, 1987; National Research Council, 2001; Rogers, 1998). Recent neuropsychological and neurobiological evidence also supports the hypothesis of a window of opportunity for intervention effectiveness in very young children at risk for mental retardation and other developmental disabilities (Bailey et al., 1999).
There are several categorical disorders that are likely to be encountered while evaluating very young children with suspected mental retardation. The disability examiner must determine whether intellectual or adaptive deficits are due to retardation or aspects of these other conditions.
Autism and Pervasive Developmental Disorders
John is a 4-year-old with delayed language and social skills development. Parents report that John is “in his own world” and has limited spontaneous speech, although he frequently repeats back exactly what is said to him. He has other unusual behaviors. These include toe walking, hand flapping, and excessive spinning of the wheels on his toy truck. John has excellent puzzle-solving skills, but he does poorly with changes in routine and seems most content when he is entertaining or playing by himself for long periods of time. During formal testing, John often seemed inattentive and his obtained total test score (IQ) of 55 on the Stanford-Binet, Fourth Edition, would seem to be an underestimate of his true intelligence.
Autism, currently classified as a pervasive developmental disorder
with symptoms that are present by 3 years of age, classically involves disturbances of: (1) social interaction, (2) communication, and (3) behavior. Autism differs from mental retardation in that intellectual deficits may or may not be apparent, but social, communication, and behavior disorders are always noted. Difficulties with social interactions include avoidance of eye contact during social activities, difficulty developing peer relations, excessive self-directed play, or avoidance of shared activities. Communication deficits may include unusual speech prosody (e.g., atypical intonation, cadence, or inflection; immediate or delayed echolalia; perseveration; lack of spontaneous speech; or difficulty with pragmatic language initiation). Behavior difficulties noted in autism include repetitive stereotypies (e.g., hand flapping, toe walking, rocking); extreme difficulties with changes in routine; and limited imaginative play or preoccupation with parts of toys (e.g., spinning the wheels of a truck rather than imaginative play with the whole truck) (American Psychiatric Association, 1994; Stone, 1997; Volkmar et al., 1994, 1997, 1999; Wolraich et al., 1996).
A recent review of 23 surveys focusing on autism and including over 4 million individuals reported a median prevalence of 5.2 per 10,000 population (95 percent confidence interval 4.5-5.5 per 10,000; Fombonne, 1999). Prevalence rates appear to have increased in recent years, presumably due to improved early identification and changes in case definition, but additional research is needed to confirm this. On average, there are 3.8 times as many males as females with autism (Fombonne, 1999).
Distinguishing whether mental retardation is present in individuals with autism is challenging, due in part to limitations in communication skills and social interaction deficits of the affected individuals (Arnold et al., 2000), as well as the diverse etiological and symptomatic expressions of the disorder. Nevertheless, Fombonne (1999) recently reported that an estimated 80.3 percent of 1,533 children with autism also had mental retardation. Estimates indicated that approximately 29 percent had mild to moderate mental retardation and 42 percent had severe to profound mental retardation. While the overall propor-
tion of male to female cases with autism was reported to be 6:1 among the subgroup with higher cognitive functioning (n = 800), this ratio dropped to 1.7:1 among the subgroup with moderate to severe mental retardation (n = 748). These data suggest that there may be gender differences in the underlying causes of disability among these two subpopulations.
Clearly, a child who has significant adaptive behavior deficits but a full-scale IQ in the 76 to 85 range would not be eligible for SSI support because of mental retardation but would be eligible instead because of his or her diagnosis of autism. Once a diagnosis of autism or mental retardation is made, no further diagnostic information is needed for the disability determination process.
Pervasive developmental disorder, not otherwise specified (PDD NOS) shares many characteristics with autism, including marked impairment of communication, social interaction, and stereotypic behaviors. However, individuals with this disorder do not meet specific diagnostic criteria for autism, Rett’s disorder, childhood disintegrative disorder, Asperger’s disorder, schizophrenia, or avoidant personality disorder. While clear deficits exist in social, communication, and other skill areas, they are generally less severe than those seen in classical autism (Fombonne, 1999; Volkmar et al., 1999). Prevalence estimates range from 1.9-16.3 per 10,000, with a median base rate of approximately 8.8 per 10,000. This indicates that pervasive developmental disorder occurs more than twice as frequently as autism (Brask, 1970; Burd et al., 1987; Cialdella & Mamelle, 1989; Fombonne, 1997, 1999; Fombonne & du Mazaubrun, 1992; Hoshino et al., 1982; Lotter, 1966).
There have been very few systematic outcome studies of children with pervasive developmental disorder or of its comorbidity with mental retardation. Available data suggest that the prognosis for individuals with this disorder is better than for those with autism (Smith et al., 2000), but difficulties persist in the social, communication, and behavioral domains. These children may also be at higher risk for emotional disabilities in later life (Towbin, 1997; Volkmar et al., 1999). As with
autism and the other disorders reviewed in this section, pervasive developmental disorder may coexist with mental retardation. The process of differential diagnosis helps determine the correlates and consequences of various syndromes.
Autism spectrum disorders (autistic disorder, pervasive development disorder-not otherwise specified, Asperger’s disorder, and childhood disintegrative disorder) are listed among the conditions qualifying for SSA disability benefits. Therefore, a diagnosis of one of these conditions or of mental retardation is sufficient for eligibility for SSI if income standards are met. It must be remembered that symptoms can be subtle in some cases of autism spectrum disorders, and when such cases are identified, the additional impact of intellectual limitations can be quite substantial. Therefore, it is imperative to consider the combination of multiple mild impairments that together may result in significant overall disability.
Tina is an 18-month-old who was born 12 weeks prematurely. Birth weight, height, and head circumference were appropriate for her gestational age. Tina had an intraventricular hemorrhage (bleeding from the interior of the brain) when she was 1 week of age. Parents report that Tina has not developed motor skills like her older sister. Her legs are stiff and she cannot sit up by herself, although she is able to roll and creep on her belly to move around. She seems very happy, has begun to babble, and seems to be trying to say a few words, although her speech is not fully intelligible. Tina’s performance on the Bayley Scales of Infant Development indicated a developmental quotient of 70, but her long-term prognosis, and whether or not she will be able to live and work independently in the community, are unclear.
Cerebral palsy is a disorder of the central nervous system that affects the posture, movement, and muscle tone of the individual. It is caused by a static insult to the brain. Children with cerebral palsy have persistent motor delays and associated cognitive, behavioral, neuro-
sensory, and orthopedic abnormalities, which may change with age. Cerebral palsy is classified as: (1) spastic cerebral palsy (65 percent), including diplegia (30 percent), hemiplegia (30 percent), and quadriplegia (5 percent); (2) dyskinetic (choreoathetoid) (19 percent); and (3) ataxic (10 percent) (Palmer & Hoon, 1995). The prevalence of cerebral palsy is estimated at 2 per 1,000 live births. An increase in cerebral palsy among low birth weight infants has been documented during the last decade, attributable to the decreased mortality in this group (Palmer & Hoon, 1995).
The estimated overall prevalence of mental retardation among children with cerebral palsy varies from 30 to 77 percent. Hemiplegia and diplegia are associated with relatively higher cognitive functioning compared with other types of cerebral palsy (Palmer & Hoon, 1995). In a recent study of 12,709 children with cerebral palsy, 61 percent were found to have no, mild, or moderate mental retardation, while 39 percent had severe to profound mental retardation (Strauss et al., 1998). Differential diagnosis is important for determining eligibility for those individuals whose cerebral palsy is very mild and who have borderline intellectual functioning or mild mental retardation (i.e., full-scale IQs ranging from 60 to 80). The motor deficits may make performance of some tasks on intelligence tests difficult or impossible. Accommodations in the testing procedures and motor-free intelligence tests may be helpful in determining these individuals’ intellectual potential (see Chapter 3). For individuals with severe cerebral palsy, motor impairments meet disability criteria for SSI eligibility.
Jimmy is a 5-year-old who was developing normally until he reached 4 years of age, when he was noted to have deterioration of expressive and receptive language skills and onset of behaviors similar to children with autism. Jimmy was noted to have decreased social interaction, limited initiation of speech, and staring spells.
Seizures are alterations in motor, behavior, consciousness, or sen-
sory function caused by repetitive, simultaneous electrical activity of the nerve cells in the brain (Vining & Freeman, 1996). Epilepsy is diagnosed when the individual has recurrent seizures. Nonfebrile seizures occur in 0.5-2 percent of children, while epilepsy occurs in 0.5 to 1 percent of children. There are two large categories of seizures, namely, generalized seizures and partial seizures. Generalized seizures include grand mal (tonic-clonic) seizures and petite mal (absence seizures), while partial seizures arise from focal areas of the brain and their manifestations usually are associated with the area of brain disturbance. Seizures may end with a postictal period in which the individual is partially or nonresponsive and may have accompanying neuromotor deficits, such as weakness of the arm.
Seizure disorders are more frequent in children with other developmental disabilities (Vining & Freeman, 1996). Children with mental retardation have a 5-10 percent incidence of epilepsy (Hauser & Hesdorffer, 1990). Of the children with mental retardation who have other neurological disorders, 40-50 percent of children with cerebral palsy and 70 percent of children with postnatal brain injury have epilepsy (Goulden et al., 1991). West syndrome (infantile spasms), Lennox-Gastaut syndrome, and Aicardi syndrome are epilepsy syndromes frequently associated with a high risk for mental retardation. Neonatal seizures are usually associated with central nervous system abnormalities as well as increased risk of mental retardation, cerebral palsy, and epilepsy (Painter & Gaus, 1991).
Landau-Kleffner syndrome, or acquired epileptic aphasia, is a rare presentation of epilepsy in childhood in which children show progressive loss of speech and epilepsy. These children may be difficult to diagnose because of their previously normal development and their slow progressive loss of receptive and expressive language skills, making psychological testing both challenging and variable over time. Children with Landau-Kleffner syndrome may be misdiagnosed as having mental retardation or autism. An electroencephalogram (EEG) that is markedly abnormal over the left temporal region of the brain helps to make this diagnosis. Unless entirely controlled through medication,
seizure disorders may affect learning capacity from preschool through high school and, ultimately, employability.
Hearing loss in children is often a silent and hidden disability that can lead to speech, language, and cognitive delays in the absence of appropriate intervention. One in 1,000 children are born with profound hearing loss, while 2 in 1,000 will acquire deafness during early childhood. And 95 percent of acquired hearing loss is attributable to middle ear infections (Northern & Downs, 1991). Hereditary hearing loss occurs in 1 in 2,000 to 6,000 children, caused by over 70 syndromes, with about 90 percent of hearing loss inherited as an autosomal recessive disorder, often with siblings involved (Konigsmark & Gorlin, 1976).
A report from the Institute of Medicine (1974) concluded that a hearing loss of 15 dB or greater (500-2,000 Hz) represents a significant impairment. By this definition, 2.2 percent of children ages 4-11 were found to have bilateral hearing losses. Losses of 15 dB may result in language delays probably due to the inability to hear the unvoiced consonants: s, p, t, k, th, f, and sh. Thus, assessment of developmental skills may be challenging in some children, even with mild hearing deficits, due to lack of constancy of auditory cues, confusion of acoustic parameters in rapid speech (e.g., understanding directions), difficulty with perceiving speech sounds, and poor mastery of grammatical rules and meanings (Northern & Downs, 1991). A child is considered deaf when there is a 70 dB or greater hearing loss. Even in these cases, if hearing loss is an isolated disability and no other factors limit cognitive development, successful academic experiences, including college and independent adult employment (Batshaw & Perret, 1992), can be expected. However, many individuals with hearing impairment experience developmental delays, and differential diagnosis is necessary to determine whether poor preschool achievement or suspected cognitive impairment is due to mental retardation or to hearing loss.
The incidence of blindness in childhood, estimated to be about 1 in 3,000 (Foster, 1988), is defined as visual acuity in both eyes of less than 20/200 or a visual field of less than 20° despite correction with eyeglasses. Causes of blindness include congenital infections and malformations, injury, prematurity, postnatal infections, vitamin deficiencies, and tumors. Approximately half of all children with blindness have other developmental disabilities (Warburg et al., 1979). Children with early onset blindness frequently have developmental delays in gross and fine motor functioning, adaptive skills, and language (Dekker & Koole, 1992; Frailberg, 1977; Pring, 1984; Teplin, 1983). These children also often exhibit unusual behaviors and self-stimulation (Good & Hoyt, 1989).
Cognitive testing is difficult in children with blindness, especially before they reach age 5, when verbal subtests of individually administered intelligence tests (e.g., Wechsler Intelligence Scale for Children-III—WISC-III) can provide valid estimates of intellectual development in the absence of language impairment. While children with visual impairment may have difficulty with abstract concepts, they often do well with numerical computation (Batshaw & Perret, 1992). As with hearing loss, differential diagnosis is important for determining the underlying reasons for any delays in cognitive development and poor preschool achievement.
The U.S. Department of Education (1999) estimates that there are currently over 5 million children receiving special education under the Individuals with Disabilities Education Act (IDEA). Methods appropriate for evaluating school-age children (K-12), diagnosing mental retardation, and determining SSI disability status have been in place for many years. However, the current social and political climate tends to limit both the number of mental retardation diagnoses and place-
ments in designated special education programs because these actions may be considered to be stigmatizing.
As mentioned earlier, there is wide variation in state special education policies regarding placement and classification of individual students. Nationally, the numbers of students identified as having a learning disability have been increasing while numbers of students identified as having mental retardation have been decreasing (Lyon, 1996), and this has serious implications for the process of determining eligibility for SSI support. Many children who in the past might have been diagnosed with mental retardation are now being classified otherwise (e.g., learning disability) and therefore have a diagnosis that is not currently included among SSA’s listing of categorical disabilities. In addition, many students with less severe impairments who in past decades would have received special education services may now complete their schooling in regular classroom programs. Thus many young adults with mental retardation may not be on SSI rolls, and after completing their schooling may not know of the benefits available to them.
The conditions complicating the diagnosis of mental retardation in young children reviewed earlier continue to be a concern throughout childhood. However, in contrast to the situation during early development, the demands of schooling provide the opportunity for recognizing academic difficulties. Clinicians and educators typically have access to methods for identifying most complicating conditions; they should therefore be able to determine the factors that are contributing to poor performance in the classroom or during assessments. Nevertheless, disability examiners must now face the task of making differential diagnosis among learning disability, mild mental retardation, attention deficit hyperactivity disorder, borderline intellectual impairment, and SSI-eligible mental retardation. This is the topic of the next section.
Mild Mental Retardation Versus Learning Disability
Clear criteria for differentiating learning disabilities from mental retardation are provided in both the DSM-IV and the International
Classification of Diseases and Related Health Problems, Tenth Revision (ICD-10) (World Health Organization, 1993). Children with specific learning disabilities show academic underachievement relative to their composite IQ. Specific learning disabilities may occur in basic reading (decoding), reading comprehension, mathematics reasoning, mathematics calculation, written expression, oral expression, and listening comprehension. Severe forms of specific learning disability may result in illiteracy, failure to understand the most basic of mathematical concepts, or inability to write. These disabilities can interfere with the individual’s ability to maintain gainful employment, and estimates indicate that they may affect 4 percent or more of the overall population (U.S. Department of Education, 1999).
While impairments limited to a specific cognitive domain are characteristic of learning disabilities, mental retardation is associated with a substantially broader profile of deficits. There are, however, rare cases of individuals with a diagnosis of both mental retardation and comorbid learning disability. This occurs when there is documented performance in a specific domain that is substantially below the level typical of the individual’s composite IQ. Learning disability and mental retardation are currently usually considered to be mutually exclusive diagnoses, although this is changing with learning disability being increasingly thought of as low achievement, rather than in terms of a discrepancy between achievement and ability. In addition, mental retardation and learning disabilities are associated with assessment profiles that are quite distinct and unambiguous for school-age individuals and adults. In fact, an IQ in the range required for a diagnosis of mental retardation is listed among the exclusionary criteria for learning disabilities. It should be noted that the term “mental retardation” has been replaced with “learning disability” throughout Great Britain, and therefore the differential diagnostic terminology is different. Nevertheless, the operational differential diagnostic criteria employed in Great Britain to distinguish specific developmental disorders of speech and language, for example, from learning disability would be comparable to DSM-IV and ICD-10 standards.
Clearly, differential diagnostic criteria are available, objectively
stated, and widely disseminated. However, advocacy and administrative policies in public school districts also influence how children are labeled, and “learning disability” is often preferred to “mental retardation.” This can reduce stigmatization, but it could also complicate SSI eligibility determination. Rather than focusing on classification provided in school records, the actual test results should be the focus of the determination process, even in cases in which children were not diagnosed with mental retardation in their school-based classification.
This is a major issue that requires broad policy attention and vigilance (e.g., MacMillan, Gresham et al., 1996). It is tacitly acknowledged in the SSI disability evaluation guidelines, in which reliance on objective evidence and variation in policies regarding special education placement are discussed (Social Security Administration, 2000). It is also illustrated by the substantial variability that exists from state to state in the numbers of school-age children classified with mental retardation (Frankenberger & Fronzaglio, 1991; U.S. Department of Education, 1994). As mentioned earlier, the question has been systematically examined in California, where school-based classifications of learning disability are made in some cases that, following accepted clinical standards, could be validly diagnosed with mental retardation (e.g., MacMillan et al., 1998).
Given this reality and the absence of learning disabilities among SSA’s listing of qualifying conditions, a considerable number of people who truly have less severe mental retardation, and both need and are legally eligible for support, may not be judged to meet eligibility requirements by some examiners unless the procedures for defining functional equivalence are clearly stated and uniformly implemented. Mild intellectual impairment is not, however, a condition that automatically prevents employment. Indeed, these individuals are the most likely candidates among the population of individuals with mental retardation to be gainfully employed. Nevertheless, there is a clearly increased risk that they will have difficulty achieving and maintaining employment after high school (Sitlington, 1996).
Melissa is an 8-year-old referred for academic underachievement and
increasing moodiness. She is currently clumsy, her attention is variable, and she frequently daydreams. Her early developmental history indicated delay in learning to tie her shoes and articulation difficulties requiring speech therapy. She had difficulties with prereading skills during kindergarten. Despite tutoring and 1.5 hours per night of homework, she did not attain the skills needed to pass 1st grade. While repeating 1st grade, she is still having trouble with her reading lessons. Melissa guesses at words and does not exhibit a phonetic approach to reading, and despite a standard score in reading of 67, she scores in the borderline range on the WISC-III (composite IQ = 71). She demonstrates poor attention as measured by a continuous performance task, and she shows evidence of a graphomotor disorder that limits her ability to write. There is some suspicion of possible mental retardation, but specific language impairment seems more likely.
Melissa would probably not meet SSI eligibility criteria based on these findings, but additional evaluations might provide sufficient documentation of substantial impairments and perhaps mental retardation. In any case, she seems to be falling further and further behind her peers, and if she does not qualify for support now, her impairments may meet eligibility criteria in the future.
Borderline Intellectual Functioning
A substantial number of children experiencing academic difficulties will be found to have composite IQs of 71 to 85 with relatively homogeneous performance profiles consistent with their overall level of intelligence. In the absence of substantial adaptive deficits, these cases will fail to meet clinical diagnostic criteria for either mental retardation or learning disabilities. According to the DSM-IV, a classification of borderline intellectual functioning may be appropriate in these cases as long as the composite IQ falls between 71 and 85. However, there is no alternative SSI classification for individuals with composite IQs of 71-85 without associated functional limitations, and therefore these individuals do not meet SSI eligibility criteria for mental retarda-
tion. Borderline intellectual functioning is not a disability in and of itself. However, it can coexist with another condition (or conditions) and contribute to the performance difficulties of children and adults associated with pervasive developmental disorders, cerebral palsy, or sensory impairment. Thus, its presence should be considered a contributing factor when other disabling conditions are also present.
HIGH SCHOOL YEARS AND ADOLESCENCE
Adolescence is a period of particular developmental significance, encompassing the transition into young adulthood (Corbett & Barton, 1992; Marshak et al., 1999; McCullough & Rutenberg, 1988). Most people consider adolescence to end at around age 18 (roughly corresponding to expected graduation from high school), but individuals with mental retardation experience developmental delays that can extend their adolescence, as well as their high school education, through age 22 (Individuals with Disabilities Education Act, 1990, 1997). The vast majority of individuals have had the presence of any developmental disabilities identified by the time they reach adolescence. Nevertheless, this is a time of heightened opportunities but also of new risks. Sherrod et al. (1993) note that the rate of change during adolescence may create “special vulnerabilities and opportunities for intervention” (p. 218). For individuals with mental retardation or borderline intellectual functioning, the developmental changes typical of adolescence (emancipation, self-concept, use of leisure time, sexuality, vocational preparation, independent living) will be, to varying degrees, affected by their inability to achieve cognitive, communicative, social, and behavioral milestones. The stresses of normal adolescence may be amplified substantially for these individuals as they progress toward young adulthood (Marshak et al., 1999), or they may persist to ages later than those typically associated with the chronological end of adolescence.
People with certain mental disorders besides mental retardation are categorically eligible for SSI and DI benefits. Individuals with mental retardation are at increased risk for such psychiatric illnesses and
severe behavioral or emotional dysfunction (Goestason, 1985; Koller et al., 1982; Menolascino & Fleisher, 1991; Nezu et al., 1992; Pfeiffer & Baker, 1994; Rutter et al., 1976). They also are vulnerable to the full range of psychopathology that occurs in the general population (Campbell & Malone, 1991; Eaton & Menolascino, 1982; Galligan, 1990). Psychiatric impairment and extreme maladaptive behavior can complicate the diagnosis of mental retardation. There has been little study of the association between risk of specific psychiatric disorders and age in individuals with mental retardation, but later adolescence through young adulthood generally represents a high risk period for many disorders (DSM-IV). Furthermore, this increased risk appears to be similar across Hispanic and non-Hispanic white Americans (Karno et al, 1987; Vernon & Roberts, 1982). Thus, behavioral or psychiatric conditions can contribute to the degree of disability, and with respect to SSI eligibility determination, this can be a particularly important factor for individuals with mild mental retardation.
Prevalence estimates for psychiatric or behavior problems vary widely for the population with mental retardation (Dykens, in press), depending on the methods used to ascertain cases (e.g., hospital patients, epidemiological samples, state systems) and the methods used to measure psychopathology (e.g., behavioral checklists, psychiatric interviews). Among referrals to a psychiatric clinic, for example, as many as 87 percent of children with mental retardation have been reported to meet criteria for one or more psychiatric disorders (Philips & Williams, 1975), but this clearly represents a subpopulation at elevated risk. Larger and more representative samples consisting of all consumers served by the California (N = 78,603) and New York (N = 30, 578) statewide mental retardation service systems found that 10 to 15 percent of individuals had significant psychopathology (Borthwick-Duffy & Eyman, 1990; Jacobson, 1982). Other studies using epidemiological approaches have reported rates of psychopathology ranging from 30 to 40 percent (Einfeld & Tonge, 1996; Reiss, 1990; Rutter et al., 1976). Clearly, a substantial subpopulation of individuals with mental retardation have significant psychiatric problems, but rates are
much higher when salient behavioral disorders are included (Jacobson, 1999). The exact numbers of people with less severe intellectual impairments or mild mental retardation and comorbid psychiatric disorders are hard to estimate. Some advocates assert that these individuals are disproportionately represented among the homeless and chronically unemployed or in the criminal justice systems, while others argue that they are remarkably resilient and manage to meet basic needs.
The heightened risk of psychiatric disorder has been variously attributed to the intellectual, medical, physical, or sensory disabilities associated with mental retardation. These include difficulty in processing information, poor social judgment, poor ability to communicate, inability to self-regulate, and inability to reason beyond the here and now (Menolascino & Fleisher, 1991). Although individuals with mental retardation experience the same range of psychiatric difficulties as other individuals, the risk for specific problems varies across the population. Persons with severe retardation, for example, are more likely to be diagnosed with behavior disorders (Borthwick-Duffy, 1994; Einfeld & Tonge, 1996; Jacobson, 1982), while those with less severe intellectual impairments are more likely to receive conventional psychiatric diagnoses (Einfeld, 1992; Matson et al., 1988).
In addition, it is often difficult to separate the diagnosis of a behavior or mental health disorder from a behavioral characteristic linked to specific genetic (e.g., Prader-Willi syndrome) or nongenetic (e.g., fetal alcohol syndrome) conditions associated with mental retardation (McIntyre et al., 2002). Such variability among individuals bearing the label of “dual diagnosis” underscores the importance of obtaining appropriate psychiatric consultation and screening for at-risk individuals, and not attributing their aberrant behaviors directly to intellectual status. In some cases, successful treatment of dually diagnosed individuals can produce substantial improvements in performance. In fact, over time, effective treatments may be of sufficient benefit to change eligibility status, especially for individuals with less severe symptoms. Therefore, disability examiners must determine from the available assessment data if there is a realistic likelihood that treatment of second-
ary disorders will produce this type of improvement, and for redetermination purposes, the time course over which possible improvements would be likely to occur.
As adolescents make the transition from school to work settings, intellectual and adaptive behavior demands can increase, as do the consequences of maladaptive behavior. There is evidence that suitable supports are difficult to find for individuals with a diagnosis of both intellectual/cognitive and psychiatric impairments (Baker et al., 1993, 1996; Szymanski, 1987). These individuals are more likely to fail in community, residential, and work placements (Borthwick-Duffy & Eyman, 1990; Campbell & Malone, 1991; Galligan, 1990; Shoham-Vardi et al., 1996), indicating that individuals with mental retardation and psychiatric disorders or other behavior problems will fare considerably less well once they are adults, as demonstrated by the following case.
Daniel is an 18-year-old nearing the completion of high school. Daniel has been diagnosed with mental retardation almost since his first day of school and has been receiving special education services since preschool. The last time Daniel was tested, he had a composite IQ of 72 and was reading at the 2nd-grade level. Daniel is quite verbal but has clear deficits in communication and social awareness. Over the past few years, Daniel has been teased and picked on by his peers and has had problems controlling his anger in response to the teasing. Because his language and social skills are limited, he has difficulty communicating his frustration and resorts to inappropriate expression of his feelings by hitting, pushing, or impulsive rages. When referred for additional assessment, Daniel’s scores on a widely used screening instrument indicated that he may have a psychiatric impairment and that further evaluation is needed. His transition teacher has had difficulty finding job placements in the community for him because of his impulsive and, at times, explosive behavior patterns. Although Daniel is approaching his formal transition from secondary school, a postschool plan has not been solidified.
The future employability of young adults with mental retardation is clearly influenced by the preparation they receive during formal
schooling. Since 1990, the IDEA has mandated that schools develop a transition plan for all eligible students, which by definition includes all individuals with mental retardation regardless of severity. In developing an individualized transition plan, school personnel complete a vocational assessment and interview of the young adult or his parents to determine preferences and skills as well as the profile of disability (Grigal et al., 1997; Miner & Bates, 1997; Wehman, 1996). This process may also present an opportunity to obtain definitive diagnostic assessments that utilize community standards for classification of disability conditions. The transition process includes generating a plan that is intended to prepare students as effectively as possible for future employment success during adulthood. However, the success of these efforts will be influenced by a number of individual characteristics, including age, gender, physical health, cognitive functioning, adaptive behavior, and maladaptive behavior or psychiatric status of the participating individual (Blacher, 2001).
The same conditions that make differential diagnosis of mild mental retardation difficult can have a negative influence on transition, as can maladaptive behavior and psychiatric problems (Blacher, 2001). Ironically, more mildly affected individuals may not receive as much transition programming and preparation for employability as their more severely disabled counterparts because they are in regular classrooms, often struggling with the more traditional academic curriculum (Sitlington, 1996). Furthermore, untreated or inappropriately treated psychiatric disorders can severely limit employability, community integration, and general quality of life. Unlike their fellow students in regular classrooms, individuals with mild mental retardation have fewer cognitive resources to compensate for their psychiatric difficulties, and after they exit formal schooling they can lose touch with mental health or mental retardation service systems.
Wehman (1996) has indicated that approximately 200,000 individuals who had participated in special education exit the public school
system each year. This highlights the fact that there is a substantial population of adults who, at least at some time, had a recognized intellectual impairment with a substantial impact on their achievement. Virtually everyone with more severe mental retardation will have been identified appropriately by the time they reach adulthood. In these cases, differential diagnosis should no longer be an issue for determination of SSI eligibility. However, the situation is very different for adults with milder forms of mental retardation and for younger adults.
Young adults who have recently turned 22 and left public high school should have recently been assessed to develop a transition plan to identify their work-related skills and to arrange for the involvement of another social service system once they depart public school. For example, regional centers were created in California to provide continuing services and supports. This system provides opportunities for state agencies responsible for follow-through services with these adults to evaluate each individual’s status vis-à-vis SSI criteria for eligibility and establish a record that could be useful for SSA staff should an application for support be made at a future date.
For older adults with mild mental retardation, who have long since left high school, the situation is quite different. Many have probably vanished from the service delivery system, in part because the formal structure of educational settings that encourages systematic assessment is no longer available. Evaluation of academic skills and any other formal testing is unlikely to occur in the normal course of adult activities, and therefore there will be no opportunity to document intellectual impairment. This is especially problematic for older adults who come from families eligible for SSI support based on economic considerations, given their tendency to have limited access to services, as in the following case.
Marlene is a 36-year-old woman with mild mental retardation living in the community with her parents. Marlene completed high school 18 years ago after struggling through regular and special education classes. Transition activities were not yet part of the school curriculum, and therefore she did not receive any vocational, social, or daily living skills training. Once Marlene exited school, she remained at home with her parents
and received no outside assistance as she sought employment. Since then, Marlene’s parents, despite their own economic hardships, have continued to take care of her everyday needs, so they never were concerned about her lack of independence. Marlene has floated in and out of sheltered workshop settings but never found her niche. Her parents are now reaching ages when they are increasingly concerned about who will care for their daughter when they are no longer able to meet her needs. Marlene does not have any marketable job skills, and although her parents are very worried, they are doing little at the present time to plan for their daughter’s future.
Adults with mental retardation who become economically independent of their families may become eligible for SSI supports themselves. If they have IQs below 60, these individuals would qualify for SSI support virtually without exception, as long as they have problems obtaining or maintaining employment. In these cases, the issues relevant to differential diagnosis are comparable to those mentioned for the school-age population with severe impairments. However, for more mildly affected individuals, there is a reasonable likelihood that they will have received a diagnosis other than mild mental retardation earlier on, and so they will not have established their eligibility for benefits under the mental retardation categorical listing. Especially careful assessment and consideration of functional equivalence will be required of the disability determination specialist to determine the eligibility of such an individual.
Considerations of psychiatric impairment or a dual diagnosis, as delineated fully in the section on adolescents, apply to adults with mental retardation as well. However, there are several additional challenges, particularly for older adults who left high school prior to 1990 and the initiation of the concept of transition planning. One is finding adults with disabilities once they have left the school system and no longer bear a school-based classification (e.g., mild mental retardation, learning disability). The second challenge is to ensure that these individuals get a complete reassessment in order to determine their eligibility for SSI. This is imperative, given evolving definitions of mental
retardation and developmental disability, as well as classification practices (MacMillan et al., 1998). Finally, adult sons and daughters of non-English-speaking parents may not routinely come to the attention of disability examiners. If these individuals have not participated in special education during their school years, they may be invisible to the service systems until some unanticipated event forces the need for direct support.
In developing the differential diagnoses for mental retardation, it is important to ensure that assessment instruments are culturally appropriate for the individual being evaluated (Sattler, 1988; Witt et al., 1998) and to clarify the relationship between culture and achievement as much as is feasible (Gallimore & Goldenberg, 2001). In addition to the influence of the majority culture and the English language, some standardized intelligence and adaptive behavior tests require social knowledge that may not be relevant in a given minority culture (Golden, 1990). Recent attempts to develop standardized tests of intelligence and adaptive behavior that are not culturally biased are described in Chapters 3 and 4.
In developing a differential diagnosis for mental retardation, particularly mild retardation, examiners need to determine whether evident psychopathological conditions are related to a specific cultural process. For example, Asian families may believe that emotional problems like anxiety bring shame and guilt to the family, and so may not disclose them (Cuellar & Paniagua, 2000). Paniagua (1998) has pointed out that, in some Hispanic cultures, mental or physical problems in a child may be thought to be the result of an extremely frightening or startling experience. These, as well as other attributions about the behaviors of their children with mental retardation (Chavira et al., 2000), can obscure the presence of a dual diagnosis or lead to a diagnosis other than mental retardation.
Clearly, examiners should be sensitive to the beliefs, attitudes, and practices related to a specific culture or religion that might be compatible or incompatible with assessment methods, employment interventions, and prioritization of goals (McAdoo, 1995; Rogers-Dulan & Blacher, 1995). In Hispanic families, for example, cultural values of family cohesion may conflict with policies promoting community inclusion and independent employment of persons with mental retardation, especially in integrated settings (Blacher et al., 1997).
Specific Disorders Associated with Mental Retardation
A complete differential diagnosis of mental retardation should address all possible disorders that share similar signs and symptoms with mental retardation. Consideration of the cause of an individual’s intellectual disability may be important for treatment and counseling. Classification systems have emphasized both function (behavior) and etiology (biomedical) dimensions since the early 1960s (e.g., Heber, 1961). However, the importance of establishing the cause of disability has not been a major focus of this chapter because it is not one of SSA’s priorities for this study. Since discussion of specific disorders associated with mental retardation may assist SSA eligibility determination specialists in evaluating individuals applying for SSI under the diagnosis of mental retardation, they are described briefly here.
Many of the issues that complicate functional and cognitive assessment or limit functional diagnostic precision, especially in infants, toddlers, and preschoolers, have already been discussed. These are serious concerns that could, at least in some cases, be addressed by refocusing attention to the underlying causes of mental retardation. There is currently an explosion of knowledge in the biomedical sciences, especially genetics and neuroscience, and this is allowing a constantly expanding diagnostic capability. Innovative technologies are now available to determine if conditions frequently associated with mental retardation are or are not present, and while their presence does not always result in substantial disability, failure to achieve eco-
nomic self-sufficiency may be the rule rather than the exception. Therefore, as in the case of Down syndrome, SSA might consider including conditions with a high probability of causing mental retardation or some other substantial disability in its list of conditions eligible for SSI benefits. Of course, some affected individuals will achieve economic self-sufficiency and will therefore be ineligible, but if an individual with mental retardation encounters difficulties in obtaining or maintaining employment, it seems reasonable to presume that the underlying impairment contributed significantly to the situation.
Mental retardation can be associated with genetic as well as nongenetic causes. Therefore, we have provided a brief overview of these broad categories of conditions and illustrated the issues that can arise in SSA eligibility determination for two representative conditions, Prader-Willi syndrome (genetic) and fetal alcohol syndrome (nongenetic).
There are over 750 known genetic causes of mental retardation. Collectively, these may account for as many as one-third of all cases of mental retardation (Matilainen et al., 1995; Opitz, 1996). Historically, identifiable genetic disorders were thought to cause severe to profound mental retardation, but more recent estimates suggest that 10 to 50 percent of mild mental retardation may also have a specific genetic origin (Rutter et al., 1996). Nonspecific genetic factors associated with individual differences in intelligence, another topic of considerable contemporary debate (e.g., Neisser, 1998), are not discussed here.
Among the relatively few disorders that have been studied to date, variability in impact on cognitive and adaptive functioning has been noted. Thus, IQ levels in individuals with disorders like fragile X syndrome, Williams syndrome, velo-cardio-facial syndrome and Prader-Willi syndrome can range widely (see Dykens et al., 2000 for a review). Like their counterparts with severe disabilities, however, high-functioning persons with these and other syndromes are likely to have char-
acteristics that compromise their employability (e.g., intellectual impairments, specific maladaptive behaviors, or psychiatric disorders).
Prader-Willi syndrome is perhaps best known for its association with eating disorders. Whereas affected babies invariably have pronounced feeding difficulties, they typically develop hyperphagia and food-seeking behaviors (e.g., foraging and hoarding) during early childhood (Dykens & Cassidy, 1999). Without lifelong dietary management, affected individuals invariably become morbidly obese and weight-associated complications remain the leading cause of death for people with this syndrome.
While the vast majority of people with Prader-Willi syndrome are invariably preoccupied with eating and food, some also show a host of nonfood obsessions and compulsive behaviors, suggesting increased risk of full-blown obsessive-compulsive disorder in this population (Dykens et al., 1996). Persons with Prader-Willi syndrome also have adaptive skills that typically fall considerably below their measured IQ (Dykens et al., 1992). Compared with others with mental retardation, children and adults with Prader-Willi syndrome show high rates of temper tantrums, aggression, stubbornness, underactivity, excessive daytime sleepiness, and emotional lability (Dykens & Kasari, 1997; Dykens & Smith, 1998; State et al., 1999). Approximately 32 percent of people with the disorder have IQs of 70 or higher. Nevertheless, higher IQ individuals are extremely likely to have poor adaptive behavior and show the same behavioral and food-related vulnerabilities as their peers with lower IQs. Regardless of their IQs, persons with Prader-Willi syndrome share the same needs for intensive support. In the employment arena, most adults with Prader-Willi syndrome are not employed competitively, and low job retention is invariably associated with aggression, tantrums, and compulsive food-seeking (Dykens, 2002). In light of these findings, several states have now passed legislation that deems any person with a confirmed genetic diagnosis of Prader-Willi syndrome eligible for lifelong state services regardless of his or her IQ. This may be an effective model for the SSA classification process to adopt.
Mental retardation can also be associated with a variety of causes that are nongenetic in origin. Among them are: (a) infections and parasitic diseases (e.g., congenital rubella syndrome, encephalitis), (b) deficiency diseases (e.g., congenital iodine deficiency syndrome), (c) congenital malformations (e.g., hydrocephalus), (d) neuroteratogenic exposure (e.g., fetal alcohol syndrome), (e) mechanical injury (e.g., perinatal hypoxia, traumatic brain injury), and (f) environmental deprivation. Of course, this is not an exhaustive listing, and for this discussion it is important to note only that each of these conditions can vary in its functional impact. In some cases, there may be minimal or no long-term consequences of the condition, while profound and permanent impairments may be observed in others. When the presence of one of these conditions is documented in an individual’s medical history, it can make an important contribution to the disability determination process. In many cases, an etiological diagnosis can provide a valid basis for determining if economic hardship is associated with the presence of a disability or some other circumstance. The case of prenatal alcohol exposure can serve to illustrate this point.
Fetal alcohol syndrome and alcohol-related neurodevelopmental disorders result from maternal consumption of alcohol during pregnancy. These disorders represent one of the leading preventable causes of birth defects, mental retardation, and neurodevelopmental disorders. Fetal alcohol syndrome is estimated to occur in 5.2 per 10,000 live births in the United States (Centers for Disease Control and Prevention, 1997; Cordero et al., 1994). While some individuals may be more vulnerable, perhaps due to their genetic makeup, the immediate cause is clearly a nongenetic factor.
Fetal alcohol syndrome results in characteristic facial features, including microcephaly, short palpebral fissures, thin upper lip, flat philtrum and midface, as well as intellectual impairment together with behavioral, emotional, and tone abnormalities. In one study (Streissguth et al., 1996), up to 94 percent of children and young adults with the syndrome had mental health problems, including 61 percent
with attention deficit hyperactivity disorder, over 50 percent with depression, and 29 percent with psychotic symptoms. Streissguth et al. also reported a mean IQ for their sample of children and young adults of 79, while adaptive skills were more than two standard deviations below the reference population mean.
Prenatal alcohol exposure can produce a spectrum of disorders including: (a) fetal alcohol syndrome, (b) fetal alcohol syndrome without confirmed exposure to alcohol, (c) partial fetal alcohol syndrome with confirmed exposure, (d) alcohol-related birth defects, or (e) alcohol-related neurodevelopmental disorder. The severity of impairment can also vary widely from case to case, with some individuals having severe and easily recognizable signs and symptoms and others having more subtle effects that can be difficult to recognize. In addition, when diagnosis occurs after infancy or early childhood, it can be difficult to document the linkage between symptoms and prenatal alcohol exposure convincingly, especially in individuals with milder impairments. Despite these difficulties, once signs and symptoms are evident and a diagnosis is made, it is likely that fetal alcohol syndrome (or one of the other conditions associated with prenatal alcohol exposure) will be a major contributing factor to substantial difficulties in school achievement, development of social skills, and maintenance of employment. Of course, mental retardation can be evident in many individual cases, but even in borderline situations, the other behavioral and functional impairments associated with prenatal alcohol exposure can safely be assumed to limit opportunities for achieving economic self-sufficiency. In these cases, SSA might consider the etiological diagnosis in arriving at its determination of eligibility for benefits.
CONCLUSIONS AND RECOMMENDATIONS
In reviewing the literature on the differential diagnosis of mental retardation from other disorders with similar signs and symptoms, the committee concludes that it is necessary to use multiple sources of objective data, including but not limited to, IQ test results, assessments
of adaptive behaviors, academic test results, and structured interviews, to determine whether an individual meets diagnostic criteria for mental retardation. Many neurodevelopmental and psychiatric disorders, such as autism, pervasive developmental disorder, attention deficit hyperactivity disorder, cerebral palsy, sensory impairments, and seizure disorders, are associated with mental retardation and complicate its diagnosis. Many of these disorders are currently defined as making the client automatically eligible for SSI benefits. Individuals who have mild mental retardation may be eligible for SSI, on the basis of concurrent neurodevelopmental or psychiatric disorders.
The committee also concludes that accurate evaluation of infants and very young children requires special attention to selecting and using appropriate evaluation instruments, conditions of test administration, experience of the evaluator, and concurrent medical and psychosocial risk factors.
The committee concludes that learning disability in school-age children can be differentiated from mental retardation by examining data from cognitive, adaptive, and academic testing. Children who have learning disabilities rather than mental retardation have significantly lower academic performance than their peers, but they do not meet criteria for mental retardation—i.e., they have composite IQs over 70 and performance difficulties focused in specific domains of cognitive and academic content. Like learning disability in school-age children, borderline intellectual functioning may be differentiated from mental retardation by reviewing cognitive and adaptive functioning evaluations. Children with composite IQ scores of 71-75 without the adaptive behavior deficits required for a diagnosis of mental retardation can be classified as having borderline intellectual functioning. It is the combination of composite IQs and adaptive behavior deficits as described in Chapter 5 that provides the best operational definition for mental retardation.
Research data show that adolescents and young adults with mental retardation are at high risk for developing a range of behavior disorders or psychiatric impairments. In that case, they are more accurately
described as having a dual diagnosis. Behavioral or mental health disorders can further complicate the differential diagnosis of mental retardation, frequently depressing scores on tests of cognitive or adaptive functioning. In these cases, reevaluation of the individual is warranted after treatment of the mental health disorder.
Research data also make it clear that cultural and socioeconomic background has profound effects on the assessment and the interpretation of behavior, particularly by proxy respondents. The disability examiner must take this into account as he or she prepares the client’s assessment, using other sources of data as needed for an accurate diagnosis.
On the basis of the data reviewed in this and previous chapters, the committee makes the following recommendations related to distinguishing mental retardation from other conditions with which it shares signs and symptoms.
Recommendation: Social Security Disability Determination Specialists may differentiate other conditions from mental retardation by using intelligence and adaptive behavior test criteria as outlined in the committee’s recommendations. Data, including school test results, intelligence and adaptive behavior test results, and psychiatric and medical test results, from community-based agencies (such as schools, hospitals, or clinics) can be used to inform the determination of SSA eligibility for the diagnosis of mental retardation, but the diagnoses given by community agencies should not be used.
Social Security Disability Determination Specialists may differentiate individuals with borderline intellectual functioning and learning disability from those with mental retardation by reviewing cognitive and adaptive behavior test results and determining whether the individual meets diagnostic criteria for mental retardation as recommended in Chapters 3 and 4.
Social Security Disability Determination Specialists do not
need to determine the presence or absence of mental retardation in individuals who are eligible for SSI due to other neurodevelopmental or psychiatric disabilities (e.g., autism, pervasive developmental disorder, attention deficit hyperactivity disorder, genetic syndromes, intrauterine exposure to alcohol or environmental toxins, sensory impairments, seizure disorders, or severe emotional-behavioral disorders).
Objective data on intellectual and adaptive functioning to determine mental retardation should be collected for individuals with mild neurodevelopmental or psychiatric disabilities who might have impairments that are consistent with or functionally equivalent to mental retardation.