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Hearing Loss: Determining Eligibility for Social Security Benefits 3 Assessment of the Auditory System and Its Functions In this chapter we discuss the methods used to assess the functioning of the adult claimant’s auditory system and hearing functions. We begin with an overview of the otolaryngological examination (for adults and children), describing the features of a “standard” examination based on best professional practices, and make some recommendations on how and when the examination should be performed. We then describe audiological tests and review current knowledge of audiological testing for adults, with special reference to the tests that are now prescribed by the Social Security Administration (SSA) for use in determining disability due to auditory impairment and to other tests that might be suitable for this purpose (testing of children is discussed in Chapter 7). Our conclusions and recommendations for Social Security disability determination are presented in Chapter 4. STANDARD OTOLARYNGOLOGICAL EXAMINATION SSA regulations as presented in the Blue Book (Social Security Administration, 2003) require, as part of the disability determination process, “medical evidence about the nature and severity of an individual’s impairments(s)” from either a claimant’s own physician or a consultative examiner (CE). Medical reports from either the treating physician or the CE should include (Social Security Administration, 2003, p. 11): Medical history;
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Hearing Loss: Determining Eligibility for Social Security Benefits Clinical findings (such as the results of physical or mental status examinations); Laboratory findings (such as blood pressure, x-rays); Diagnosis; Treatment prescribed with response and prognosis; A statement providing an opinion about what the claimant can still do despite his or her impairment(s), based on the medical source’s findings on the above factors. This statement should describe, but is not limited to, the individual’s ability to perform work-related activities such as …hearing…. For a child, the statement should describe his or her functional limitations in learning, …communicating. SSA regulations also require that hearing tests “should be preceded by an otolaryngologic examination.” In contrast, the committee recommends that the otolaryngological examination should follow the audiological examination (but by no more than 6 months), because a physician cannot provide a competent report, including the six elements listed above, without recent audiometric data. The appropriate source for the otolaryngological examination is an otolaryngologist certified by the American Board of Otolaryngology. Otolaryngologists specialize in disorders of the ear, nose, throat, and related structures of the head and neck and have completed at least five years of residency training following receipt of the M.D. or D.O. (doctor of osteopathy) degree. Medical History The elements of the medical history in an examination performed to provide medical evidence for SSA program eligibility are identical to those included in a routine medical examination. There are, however, some areas of emphasis worthy of mention. Chief Complaint and Present Illness: The claimant’s chief otological complaint may not be hearing loss; it may be tinnitus, vertigo, otalgia, or otorrhea. For each significant otological symptom, but especially for hearing loss, the physician should inquire about: The nature of the symptom—Are hearing difficulties noticed in one ear or both? For what types of sounds? Severity Chronology—Onset? Change over time? Fluctuation? Exacerbating and/or ameliorating factors, such as background noise Effects on activities of daily living—ordinary conversation, telephone use, work.
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Hearing Loss: Determining Eligibility for Social Security Benefits Review of Systems: Review of organ systems will occasionally reveal problems in other systems that are relevant to otological diagnosis (e.g., eye symptoms in Cogan’s syndrome). Review of systems is more likely to be helpful in cases of hearing loss with onset in childhood or in cases demonstrating rapid progression or fluctuation of hearing loss. Past Medical History: A history of mumps or measles (or of maternal rubella or cytomegalovirus) can be relevant if hearing loss began in childhood. Head injury often causes hearing loss. Most ototoxic drugs are given in the context of hospitalization for severe infections (aminoglycosides) or cancer (cisplatin and carboplatin). A history of previous otological treatment, especially ear surgery, is always relevant. Social History: A discussion of family and marital status includes communication difficulties with the claimant’s spouse or partner, relatives, and other persons. The claimant’s educational and occupational history will assist in understanding both the difficulties experienced in the workplace and the knowledge, skills, and abilities that might be useful in other jobs. Previous hazardous noise exposure may be uncovered in a discussion of both work history (including military service) and recreational activities (e.g., shooting, woodworking). If there has been significant noise exposure in the past 72 hours, audiometry should be deferred. Family History: Hearing loss or deafness prior to age 60 or ear surgery in a close relative may suggest a hereditary disorder. Clinical Findings (Physical Examination) Informal Observation of Communication: The otolaryngologist can usually directly observe the claimant’s ability to hear and understand in a communication environment similar to some workplaces: one-to-one conversation in a relatively quiet room. It is neither necessary nor desirable to do this separately from the process of obtaining a history and performing a physical examination. Instead, the claimant’s ability to hear and understand can be assessed based on informal conversation during history taking, ear examination, etc. If the claimant has either hearing aids or a cochlear implant, these should be used during as much of the interview and examination as possible. During this process, the examiner can note whether the claimant does poorly under certain conditions (e.g., inability to see the examiner’s face, increased distance from the examiner, presence of background noise, removal of hearing aids) and whether the claimant’s behavior is consistent. Any obvious language or cognitive problems should be noted. Otoscopy: Observation and palpation of the auricle, followed by pneumatic otoscopy, will usually suffice to detect outer ear and middle
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Hearing Loss: Determining Eligibility for Social Security Benefits ear abnormalities that may contribute to diagnosis. When conductive or mixed hearing loss is present, the ears should usually be examined by otomicroscopy. Tuning Fork Tests (optional): Audiometric tests usually provide un-ambiguous evidence of the type of hearing loss (conductive, sensorineural, or mixed). Nevertheless, tuning fork tests (most often, Weber and Rinne tests using the 512 Hz fork) can sometimes provide a useful cross-check on the validity of the audiometric data. This is especially true if insert earphones are not used, because collapsing ear canals can cause apparent (but spurious) conductive hearing loss, which will be absent on tuning fork testing. Head and Neck Examination: In the presence of chronic otitis media, examination of the neck, nasal cavities, and pharynx may disclose relevant findings. In congenital hearing loss, examination of the face, neck, oral cavity, and eyes may contribute to the identification of a hereditary or acquired syndrome. With these exceptions, head and neck examination is rarely helpful. Cranial Nerves (optional): The functions of the third through twelfth cranial nerves are usually tested as part of a complete otological examination, especially if there is asymmetrical hearing loss. Balance and Cerebellar Tests (optional): When the claimant’s complaints include vertigo, unsteadiness, or lightheadedness, the otological examination usually includes observation of the claimant’s gait; standing balance will be addressed with eyes open and closed. Tests of fine motor coordination and ability to determine the spatial position of body parts without vision are often used to assess cerebellar function. Laboratory Findings In most cases, the only relevant “laboratory findings” are the results of the audiological examination. In some cases of asymmetrical hearing loss, imaging tests are necessary before a firm diagnosis can be made. In rare cases of rapidly progressive or fluctuating hearing loss, blood tests for infection, immunological disorders, or other systemic disorders can be helpful. Tests of vestibular function may assist diagnosis when there are symptoms of dizziness or unsteadiness. For stable or slowly progressive symmetrical hearing loss without vestibular symptoms, laboratory tests (other than audiometry) are rarely useful in diagnosis or prognosis. Diagnosis The nature of the hearing loss (sensorineural, conductive, or mixed) is usually apparent from the audiometric data. The cause(s) are not always
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Hearing Loss: Determining Eligibility for Social Security Benefits certain, but the physician should state an opinion about causation to a “reasonable medical certainty.” In other words, the physician should identify a cause only if it is more likely than not that it contributed to the patient’s hearing loss. Treatment Prescribed with Response and Prognosis In many cases (especially when the hearing loss is conductive or mixed), medical or surgical treatment is advised. For most people applying for Social Security Disability Insurance or Supplemental Security Income because of hearing loss, medical treatment is no longer an issue. Hearing aids or cochlear implants may be advised. Prognosis (including expected response to recommended medical, surgical, or prosthetic intervention) is essential, because of the SSA standard of an “impairment which can be expected to last for a continuous period of at least twelve months.” Hearing impairment that has not been present and stable for at least 6 months will rarely meet this standard. What the Claimant Can Still Do Information collected during the history-taking and physical examination is combined with audiometric data and information obtained from previous medical and audiometric records to support an opinion regarding the claimant’s ability to hear and understand in a variety of communication settings. Children The history and physical examination described above is typical not only for adults, but also for children of school age. Some parts of the physical examination (e.g., tuning fork tests and assessment of ability to communicate) will not be feasible in very young children, who may require additional evaluations before a determination of causation and prognosis can be made. These additional evaluations may include: medical genetics, ophthalmology, pediatric neurology, and speech-language pathology. ASSESSMENT OF AUDITORY FUNCTION The basic audiometric test battery recommended by the committee includes assessment of pure-tone thresholds by air conduction and bone conduction, speech recognition thresholds, suprathreshold speech recognition in quiet and noise, and acoustic immittance measures. This pro-
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Hearing Loss: Determining Eligibility for Social Security Benefits tocol will enable the determination of the degree of hearing loss, the site of lesion in the auditory periphery, and the capacity of the individual to understand speech in typical listening environments. Many of the stimuli and procedures for conducting the routine assessment have been standardized for English-speaking adults. Modifications to this test battery are necessary for assessment of children and non-English speakers. Additional electrophysiological measures of auditory function include otoacoustic emissions (OAEs) and auditory evoked potentials (AEPs), which may be performed in place of, or in addition to, the routine audiometric measures. These tests are particularly useful for assessment of infants and young children, as well as individuals who are difficult to test. To ensure accuracy of test results, the test environment must be controlled and the test equipment must be calibrated as described in Chapter 4. Pure-Tone Threshold Audiometry Hearing sensitivity is measured separately in each ear for pure-tone signals, which are single-frequency tones generated electronically and transduced through an earphone or bone conduction vibrator. The “gold standard” of hearing sensitivity is the pure-tone audiogram, shown in Figure 3-1. The audiogram displays a listener’s detection thresholds (in dB hearing level [ANSI S3.6-1996] (American National Standards Institute, 1996) for pure-tone signals at octave frequency intervals within the range of 250-8000 Hz, in both ears. This frequency range encompasses the spectrum of speech sounds. Consequently, an average of pure-tone detection thresholds corresponds with the average threshold for speech (Fletcher, 1950). Hearing thresholds may also be assessed at selected interoctave frequencies (e.g., 3000 and 6000 Hz), particularly in cases of suspected noise-induced hearing loss. The standard method for measuring the pure-tone detection threshold is the modified Hughson-Westlake technique (American National Standards Institute, 1997; American Speech-Language-Hearing Association, 1978; Carhart and Jerger, 1959). This is a single-stimulus technique that combines ascending and descending methods of limits. Stimulus duration is 1-2 seconds, and the signal may be steady-state or pulsed (Mineau and Schlauch, 1997). The operational definition of threshold is the lowest level at which a listener detects a signal for 50 percent of the ascending runs. Pure-tone thresholds are assessed in the air conduction mode (250-8000 Hz) and the bone conduction mode (250-4000 Hz). The preferred earphones for air conduction threshold assessment are insert earphones to prevent ear canal collapse and ostensible high-frequency conductive hearing loss that may occur with supra-aural earphones
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Hearing Loss: Determining Eligibility for Social Security Benefits FIGURE 3-1 Graphic representation of a pure-tone audiogram. (Clemis, Ballad, and Killion, 1986). However, supra-aural earphones are acceptable for routine clinical use. Measurement of pure-tone detection thresholds is essential for determination of the degree of hearing loss, and it forms the basis of disability determination for SSA. A classification scheme for degree of hearing loss, shown in Table 3-1, is based on the mean air conduction pure-tone thresholds at 500, 1000, and 2000 Hz (PTA 512) (Clarke, 1981; Goodman, 1965). (PTA 512 is the pure-tone average implied in the text of this report that deals with adult hearing, unless a different frequency set is specified.) This classification scheme is appropriate if the thresholds do not vary dramatically across audiometric frequency. In the event of widely varying thresholds, the degree of hearing loss should be described separately for frequencies with minimum hearing loss and maximum hearing loss.
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Hearing Loss: Determining Eligibility for Social Security Benefits TABLE 3-1 Categories of Degrees of Hearing Loss, Based on Air Conduction Pure-Tone Average at 500, 1000, and 2000 Hz Degree of Hearing Loss Category Pure-Tone Average Range Normal hearing sensitivity –10 dB HL to 15 dB HL Slight hearing loss 16 dB HL to 25 dB HL Mild hearing loss 26 dB HL to 40 dB HL Moderate hearing loss 41 dB HL to 55 dB HL Moderately severe hearing loss 56 dB HL to 70 dB HL Severe hearing loss 71 dB HL to 90 dB HL Profound hearing loss 91 dB HL to equipment limits SOURCE: Clarke (1981). In particular, hearing loss in adults is often more severe in the higher frequencies than in the lower frequencies. This severity scale classification scheme attempts to describe the average communicative effect of a hearing loss without the use of a hearing aid. Individuals with normal hearing experience no significant difficulty hearing faint speech or speech in moderate noise levels. The category included in Table 3-1 of “slight” hearing loss has been applied traditionally to children, who experience detrimental effects of this degree of hearing loss for developing normal speech and language. Recent reports suggest the slight hearing loss category is appropriate for adults as well, because many adults with PTAs in this range complain of difficulty hearing faint speech in noise and may seek amplification (Martin and Champlin, 2000). Those with mild hearing losses experience difficulty hearing faint speech or speech from a distance, even in quiet. Moderate hearing loss is associated with frequent difficulty with normal speech (Bess and Humes, 2003); conversational speech may be heard only at close range. Individuals with a moderate-to-severe hearing loss may detect the presence of conversational speech, but are often unable to understand conversational speech without amplification, due to insufficient audibility. In addition, most energy in speech is concentrated in the lower frequencies and then decreases in the higher frequencies, coinciding with the frequency region corresponding to the most hearing loss in adults. Thus, higher frequency speech information will often be inaudible for individuals with an average hearing loss in the moderate range or even the mild range. Because most consonant phonemes in speech are composed of weak, high-frequency energy, individuals with such high-frequency hearing losses
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Hearing Loss: Determining Eligibility for Social Security Benefits may have considerable difficulty understanding speech accurately although they are able to detect the presence of speech. In addition to the loss of audibility, hearing impairment in the mild to moderately severe range is often accompanied by distortion of the acoustic signal. The detailed spectral, temporal, and intensive characteristics of the speech signal are processed differently in the impaired auditory system from in the normal auditory system. This is thought to result in considerable difficulty understanding a spoken message, particularly in challenging listening environments that include noise and reverberation (Plomp, 1986; Plomp and Duquesnoy, 1980). Individuals with a severe hearing loss (71-90 dB HL PTA in the better ear) who do not use a hearing aid cannot detect the presence of conversational speech and may hear only shouted speech. These individuals may derive limited benefit from a hearing aid, depending on their previous experience with amplification. A profound hearing loss typically is associated with extremely limited capacity to receive speech in the auditory mode. Individuals with a profound hearing loss may hear very loud or amplified sounds, but they often cannot benefit from a hearing aid for understanding speech. Hearing is not the primary communication channel for people with a profound hearing loss who do not use hearing aids or cochlear implants. Because of their limited ability to receive spoken language in the auditory-only mode, people with severe or profound hearing losses are candidates for admission to schools for the deaf, where numerous accommodations and other special services are available. For example, the application information for the National Technical Institute for the Deaf specifically states that the only audiological criterion for admission is a PTA score of 70 dB HL or greater in the better ear. Speech Audiometry Speech audiometry encompasses a range of measures that include assessment of speech thresholds, suprathreshold speech recognition in quiet, and suprathreshold speech recognition in noise. Although suprathreshold speech recognition measures are usually obtained for an auditory-only presentation mode (unisensory), they may also be obtained for an auditory + visual presentation mode (bisensory). Stimuli may be recorded or live, but only recorded stimuli can undergo standardization procedures. Recorded speech stimuli are routed through a speech audiometer to ensure accurate signal presentation levels. Standards governing the calibration of the speech signal through the speech audiometer
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Hearing Loss: Determining Eligibility for Social Security Benefits (American National Standards Institute, 1996) provide the RETSPL for speech signals.1 Speech Thresholds The pure-tone examination assesses an individual’s detection thresholds for tones that encompass the range of speech sounds, from 250 to 8000 Hz. Validity of these pure-tone thresholds can be established by verifying that these thresholds actually reflect the ability to detect speech. To that end, a threshold level for speech is obtained to assess the validity of the pure-tone audiogram. Two types of speech thresholds may be measured: the speech detection threshold (SDT) and the speech recognition threshold (SRT). The SDT is the lowest intensity level for 50 percent detection of the speech signal. The SDT normally is obtained at a level that is 8-9 dB lower than the speech recognition threshold. The SRT is the minimum hearing level of a speech signal at which a listener correctly repeats 50 percent of the spoken message. Usually the speech signals are spondee words,2 but they may be sentences. The SRT obtained with spondees corresponds with the three-frequency PTA (500, 1000, 2000 Hz) in individuals with normal hearing or reasonably flat audiograms, and with a two-frequency PTA (an average of the best two thresholds obtained between 500 and 2000 Hz) in individuals with sloping or rising audiometric configurations (Carhart, 1971; Fletcher, 1950), if the speech signal is calibrated according to the RETSPLs for speech (American National Standards Institute, 1996). The SRT is also useful for predicting the audibility of conversational speech 1 At present, recommended procedures for recordings of speech materials are available in an appendix to the ANSI S3.6 standard. These recommended procedures specify that recordings shall provide a 1000 Hz calibration tone or a weighted random noise at the beginning of the recording, at the same level as the speech materials on the recording. In addition, the international standard, IEC 60645, indicates that speech level should be expressed as the equivalent continuous sound pressure level determined by integration over the duration of the speech signals with frequency weighting C. This indicates that specified levels of the speech stimulus are based on average levels. Some recorded speech recognition materials do not conform to these standard recording and calibration procedures. For example, the Veterans Administration recordings of speech materials use a calibration tone that reflects the peaks of the carrier phrase for each test on the recording. Normative data obtained with each speech test are therefore appropriate as a reference only if the test is presented using identical procedures for calibration and test level. In order to present a standardized test, the tester should be well informed about the correct calibration procedures and presentation levels for particular speech materials. 2 Spondee words are two-syllable words with equal emphasis on both syllables, for example, “milkman” and “sidewalk.”
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Hearing Loss: Determining Eligibility for Social Security Benefits and the need for amplification (Hodgson and Skinner, 1981). Standard audiometric practice includes measurement of the SRT; the SDT is reserved for cases in which an SRT cannot be measured. Several standard methods for measurement of SRT produce reliable threshold estimates with recorded speech materials. The method recommended by the American Speech-Language-Hearing Association (ASHA) is a descending technique in which the number of spondee words presented at each step is equivalent to the step size, for either 2-dB or 5-dB step sizes (American Speech-Language-Hearing Association, 1988; Tillman and Olsen, 1973). This technique is both reliable and valid (Beattie, Forrester, and Ruby, 1977; Wall, Davis, and Myers, 1984; Wilson, Morgan, and Dirks, 1973). Measurement of speech recognition thresholds is useful for corroborating the validity of the pure-tone thresholds and is routinely conducted by most audiologists (Martin, Champlin, and Chambers, 1998). In addition, an estimate of the audibility of conversational speech without amplification can be made directly from the SRT. For example, a score in the better ear that approximates the level of average conversational speech (45-50 dB HL) indicates that everyday speech is minimally audible to the listener, and a score that exceeds 50 dB HL indicates that virtually all unamplified speech signals are inaudible to the listener unless the talker speaks loudly or approaches the listener more closely than the typical 1.0 meter distance of casual conversation. This information is useful for determining hearing aid needs and may be used to substantiate a claim for functional hearing impairment disability. Current SSA guidance prescribes testing of SRT (Social Security Administration, 2003, p. 24). Suprathreshold Speech Recognition Suprathreshold measures expressed as percentage-correct speech recognition scores indicate the clarity with which an individual receives and understands a spoken message. Although speech recognition scores are correlated with pure-tone thresholds, the correlation is typically not high enough to accurately predict one from the other for an individual, so speech recognition must be measured directly. Most speech recognition tests are presented at levels well above the listener’s detection threshold to estimate maximum potential performance. These measures are used for multiple purposes: diagnosing the auditory site of a lesion, assessing potential benefit with amplification, assessing candidacy for a cochlear implant, and assessing everyday speech understanding. SSA requires testing of “speech discrimination in quiet at a test presentation level sufficient to ascertain maximum discrimination ability”
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Hearing Loss: Determining Eligibility for Social Security Benefits TABLE 3-2 Speech Recognition Materials Available in Languages Other Than English Test Type/Language Source Bisyllables Spanish Auditec of St. Louis Luganda Nsamba, 1979 Monosyllabic Words Spanish Auditec of St. Louis Russian Aleksandrovsky, et al., 1998 Hearing in Noise Test (HINT) Spanish Cochlear Corporation, 2002 French Laroche, et al., University of Ottowa, 2002 Mandarin Wong, University of Hong Kong, 2002 Cantonese Wong, University of Hong Kong, 2002 Japanese Kubi, Osaka University, 2002 Picture Identification Spanish VA recordings: McCullough and Wilson, 1998 Trisyllabic Words (for SRT) Spanish Auditec of St. Louis Bisyllabic Words (for word recognition) Spanish Auditec of St. Louis Synthetic Sentence Identification (SSI) Test Spanish Auditec of St. Louis NOTE: Entries are publications, vendors, or contact names for obtaining each set of materials. the listener’s native language. A listing of speech recognition tests that have recordings available in languages other than English is shown in Table 3-2. Lists of Spanish bisyllabic words tend to yield performance scores by Spanish speakers that are comparable to English monosyllabic word recognition scores by native speakers of English (Weislander and Hodgson, 1989). Listener responses can be scored phonetically with reasonable accuracy even if the audiologist is unfamiliar with the test language (Cakiroglu and Danhauer, 1992; Cokely and Yager, 1993). Alternatively, a closed-set, picture-pointing task can be used for test administration in a language unfamiliar to the audiologist. This method removes any potential bias or scoring error. Tests that incorporate picture-pointing tasks on paper and computer are available in Spanish and Russian (Aleksandrovsky, McCullough, and Wilson, 1998; Comstock and Martin, 1984; McCullough, Wilson, Birck, and Anderson, 1994; Spitzer, 1980). There are many languages for which there are no recorded versions of speech recognition tests. One recommendation is to assess the speech recognition threshold using digit pairs in place of spondee words, be-
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Hearing Loss: Determining Eligibility for Social Security Benefits cause new language learners acquire knowledge of digits relatively early, and audiologists can easily score the responses (Ramkissoon, Proctor, Lansing, and Bilger, 2002). This digit-SRT test can be administered to listeners from any language, and results appear to be valid, based on high correlations between digit-SRTs and the PTA measured for nonnative English speakers (Ramkissoon et al., 2002). A comparable test for assessing suprathreshold speech recognition in listeners with various linguistic backgrounds has not been developed. Acoustic Immittance Measures Acoustic immittance measures are a series of electrophysiologic tests that assess the integrity of the middle ear system and the structures comprising the acoustic reflex pathway. Acoustic immittance measures are administered routinely as part of the standard audiometric evaluation (Martin et al., 1998), using commercially available acoustic immittance systems calibrated according to ANSI standards (American National Standards Institute, 2002a). Interpretation of the acoustic immittance test results, in conjunction with the audiogram, aids in determining the site of the lesion associated with a hearing loss. The three basic subtests of the acoustic immittance battery are tympanometry, acoustic reflex thresholds, and acoustic reflex adaptation. Tympanometry Tympanometry is an assessment of the ease of acoustic energy transfer (acoustic admittance) through the middle ear system, as a function of air pressure. In the normal middle ear system, energy transfer of the middle ear, as measured at the plane of the tympanic membrane, is maximal at atmospheric pressure (0 dekaPascals, or daPa) and is minimal at air pressures that produce a stiffening of the middle ear system (air pressures remote from 0 daPa, such as +200 daPa or –200 daPa). Tympanometry is performed by presenting a probe tone to the ear canal and measuring the acoustic admittance (in mmhos, an expression of the ease of energy flow that has a reciprocal relationship with impedance as measured in acoustic ohms) of this tone, as the air pressure presented to the sealed ear canal varies from positive to negative (usually in the range +200 daPa to -400 daPa). The standard probe tone frequency is 226 Hz, although many additional probe frequencies can be presented. The resulting tympanogram is a pressure-admittance function that depicts the admittance characteristics of the tympanic membrane and middle ear system of the test ear. Three parameters of the tympanogram can be quantified: peak admittance (Peak Y), tympanometric width (TW), and equiva-
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Hearing Loss: Determining Eligibility for Social Security Benefits TABLE 3-3 Norms for Peak Admittance (Y), Tympanometric Width (TW), and Equivalent Volume (Vec) Age Group Y (mmho) TW (daPa) Vec (cm3) Adults Mean 0.79 77 1.36 90th percentile range 0.30–1.70 51–114 0.9–2.0 Children Mean 0.52 114 0.58 90th percentile range 0.25–1.05 80–159 0.3–0.9 SOURCE: Margolis and Hunter (1999). lent volume (Vec) (American Speech-Language-Hearing Association, 1990). Normal values for each of these parameters are shown in Table 3-3. Peak admittance is the admittance value observed at the peak point on the tympanogram, in mmhos. Abnormally low values indicate a stiffening pathology of the middle ear, including otitis media with effusion and otosclerosis. Excessively high peak admittance values are consistent with a hypermobile middle ear system, such as ossicular discontinuity or scarring of the tympanic membrane. Tympanometric width is the pressure interval on the tympanogram corresponding to a 50 percent reduction relative to the peak height. It is an indication of the shape of the tympanogram. A flat tympanogram, often associated with otitis media with effusion, produces an abnormally wide TW. Equivalent volume is an indication of the volume of the external auditory canal. It is obtained at a pressure that minimizes the admittance of the middle ear (e.g., +200 daPa or -400 daPa). Thus, the height of the tympanogram at one of these values is the equivalent volume of the external auditory canal. Most acoustic admittance systems provide the Vec in a printout accompanying the tympanogram. Abnormally high Vec coupled with a flat tympanogram is observed in cases of a perforation of the tympanic membrane. In summary, abnormal tympanograms are observed for a variety of pathological conditions affecting the tympanic membrane and middle ear, including otitis media with effusion, otosclerosis, ossicular discontinuity, tympanic membrane perforation, and a scarred (monomeric) tympanic membrane. A normal tympanogram indicates the presence of a normally functioning middle ear system, either with or without normal hearing.
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Hearing Loss: Determining Eligibility for Social Security Benefits Acoustic Reflex Thresholds The acoustic reflex is a contraction of the stapedius muscle of the middle ear in response to loud sound. The pathways for this reflex ascend from the peripheral auditory system to the brainstem and then descend both ipsilaterally and contralaterally, so presentation of a loud sound in one ear results in bilateral contraction of the stapedius muscles. This contraction stiffens the middle ear system, causing a reduction in the transfer of low-frequency energy. The clinical procedure for assessing the acoustic reflex threshold involves presenting a low-frequency probe tone (i.e., 226 Hz) to one ear, presenting high-intensity signals to the same or the other (contralateral) ear, and monitoring a decrease in the acoustic admittance of the probe tone in response to the presentation of the high-level signal. The minimum stimulus level that results in an observable decrease in acoustic admittance is defined as the acoustic reflex threshold. Acoustic reflex thresholds are usually measured from 500-2000 Hz, in both ipsilateral and contralateral modes, for each ear. In listeners with normal hearing, the acoustic reflex threshold is elicited at levels approximating 85 dB HL (+/− 10 dB). The acoustic reflex is absent if the signal doesn’t reach the cochlea with sufficient intensity, if there is damage affecting any of the structures along the acoustic reflex pathway, or if there is a stiff middle ear system in the probe ear. Examples of conditions in which the acoustic reflex is absent include conductive hearing loss of 25 dB HL or greater in the stimulus ear, conductive hearing loss of 10 dB HL or greater in the probe ear, sensorineural hearing loss exceeding 75 dB HL in the stimulus ear, a lesion of the facial nerve in the probe ear, and a lesion in the auditory brainstem affecting the crossing pathway of the acoustic reflex arc. The acoustic reflex may also be absent with a lesion of the vestibulocochlear nerve in the stimulus ear, depending on the extent of the lesion. The acoustic reflex is expected to be present in cases of mild, moderate, or moderately severe sensorineural hearing loss associated with a cochlear lesion. The acoustic reflex threshold generally increases as a function of pure-tone threshold in these cases (Silman and Gelfand, 1981). Otoacoustic Emissions Otoacoustic emissions (OAEs) are noninvasive, objective measures of cochlear functioning. The cochlea contains two distinct types of sensory hair cells, outer and inner hair cells. When the inner hair cell senses vibration (sound), it will send the information by releasing neurotransmitters at its base to initiate activity in the primary auditory nerve. The outer hair
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Hearing Loss: Determining Eligibility for Social Security Benefits cell also will sense sound as vibration, but it does not send information to the central nervous system. Rather, the role of the outer hair cell is to amplify the vibration at specific regions of the cochlea by actually expanding and contracting in response to sound (Brownell, Bader, Bertrand, and de Ribaupierre, 1985; Russell and Sellick, 1978). This added vibration is imparted to adjacent inner hair cells, thereby increasing the overall sensitivity of the auditory system to weak sounds. Otoacoustic emissions are produced when some of the energy from the outer hair cells is propagated through the fluids in the cochlea back to the middle ear and tympanic membrane to create a sound wave in the external ear canal (Kemp, 1986). OAEs are highly dependent on the outer hair cells (Schrott, Puel, and Rebillard, 1991), which are generally more vulnerable to disease and damage than inner hair cells. Therefore when OAEs are normal, it is presumed that the inner hair cells are functioning normally as well. Consequently, when an OAE is recorded, one can usually assume that hearing thresholds are 30-40 dB HL or better. In addition, frequency regions of normal and abnormal outer hair cell function can be predicted by patterns of OAE response. In this way the OAE can aid in objective measures of hearing (but see caveat below). Two basic types of OAE are used clinically and both are acceptable for use in infants, children, and adults. Each type requires a small probe to be placed into the ear canal. The probe contains one or two sound production devices (transducers) as well as a microphone to record the emission itself. The transient-evoked OAE generally uses a click stimulus, but occasionally a tone burst is used. The response is spread over about 10 ms time due to travel time in the inner ear. Responses from many stimuli are averaged to reduce noise. Several types of statistical measures are used to determine the presence of a reliable response. The other type of OAE used clinically is the distortion-product OAE, which is measured in response to two tones. The interaction of the two tones produces distortion, creating a third tone at a frequency predictable from the eliciting tones. A computer presents the primary tones and analyzes the microphone output for the presence of the distortion product. For a thorough review of clinical applications of both types of OAEs, see Prieve and Fitzgerald (2002). It is important to keep in mind that an OAE can be present in narrow regions of good outer hair cell function and should be interpreted in a frequency-specific manner. As such, the OAE can help to fill in information from specific frequency regions. Caution should be used in overinterpretation of very narrow, low-amplitude regions of OAE, which can be spurious noise. Also, OAEs are not strong in low-frequency regions (1000 Hz and below) in infants and toddlers due to physiological
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Hearing Loss: Determining Eligibility for Social Security Benefits noise, and thus absent OAEs in low-frequency regions should not be given great weight in interpretation. OAE presence indicates good hair cell function and generally indicates that the hearing thresholds should be better than 30-40 dB. OAEs, however, cannot be used to determine exact hearing thresholds. In contrast, the absence of an OAE can be due to a variety of causes, from middle ear dysfunction to sensorineural disorders producing hearing loss of any degree. The absence of an OAE alone should not be interpreted as indication of significant hearing loss. There are conditions in which the presence of an OAE alone does not ensure normal hearing sensitivity. Disease that spares the cochlea and impairs function in the auditory nerve or low brainstem (for example acoustic neuroma or auditory neuropathy) can also cause significant hearing loss. The OAE therefore should not be tested in isolation but must be included in a battery of tests for accurate interpretation. Nevertheless, measurement of OAEs provides a quick, noninvasive view of the functioning of the inner ear. Because of the value of these measures, the evaluation of OAEs is routine in many diagnostic audiology settings. Auditory Evoked Potentials Auditory evoked potentials (AEPs) are recordings of neural activity evoked by sound. The AEP is collected using surface electrodes placed on the scalp and near the ear. Computer-generated sounds are presented to subjects via earphones, and each presentation triggers a synchronized recording of neural activity. The responses to many stimuli are averaged in a manner time-locked to the stimulus to reduce the contribution of nonauditory generators, such as random muscle or brain activity. AEPs occur within fractions of a second following stimulation. The earliest activity, known as the auditory brainstem response or ABR, has a latency of 0-20 ms depending on the age of the subject and the nature of the sounds used to elicit the response. This response is generated in the auditory nerve and brainstem auditory pathway. Other evoked potentials include the middle latency response (MLR), generated in the thalamus and primary auditory cortex, with a latency of 20-100 ms, and the late cortical response (LCR), generated in the auditory cortex and association areas, with a latency of 100-250 ms. While all of these AEPs can be used to predict hearing threshold levels, the one used most commonly in the United States is the ABR. In contrast, most of the audiology literature from other parts of the world supports the use of late responses for threshold estimation in adults (Coles and Mason, 1984; Hone, Norman, Keogh, and Kelly, 2003; Hyde, Alberti, Matsumoto, and Yao-Li, 1986; Tsui, Wong, and Wong, 2002). Most recently, a variation of standard evoked potential
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Hearing Loss: Determining Eligibility for Social Security Benefits technique, referred to as auditory steady-state response (ASSR), has been used successfully to predict frequency-specific hearing thresholds. The ABR is a recording of activity generated in the auditory nerve and subsequent brainstem auditory pathways. Short-duration sounds are presented to the ear through earphones. These generate a series of neural impulses in the brainstem auditory pathway. The ABR requires that the electrode-recorded activity be averaged following presentation of hundreds of stimuli. A computer time-locks the recording of neural activity to the onset of stimuli and creates an average neural response. The averaging process allows the minute (nanovolt level) changes in electrical potentials in the brainstem that occur in response to sound to be distinguished from other electrical activity in the brain and muscles of the head and neck. The ABR, when elicited by clearly audible stimuli, produces a consistent series of peaks labeled with Roman numerals I-V. In infants, only peaks I, III, and V are visible. As the stimulus level approaches the threshold of hearing, ABR peaks diminish in amplitude and number and increase in latency (see Figure 3-2). The lowest stimulus level that will produce a visually detectible ABR is termed the ABR threshold. The ABR threshold in most instances is a very good indicator of the hearing threshold that would be determined by standard audiometric techniques (Sininger, Abdala, and Cone-Wesson, 1997; Stapells, Gravel, and Martin, 1995). In the absence of neurological disease, the ABR threshold can be used to accurately predict audiometric thresholds. This is a standard technique used to predict degree and configuration of hearing loss in infants under 6 months of age and in uncooperative toddlers. It can also be used to predict hearing thresholds in adult patients who cannot or will not respond to standard audiometric testing procedures. ABRs should not be used in isolation; rather, they should be part of a test battery including otoacoustic emissions, middle ear assessment, and some observation of behavior in response to sound (see Chapter 7). In addition, when the auditory nerve or low brainstem is specifically impaired, the ABR threshold may not be an accurate indicator of hearing threshold (Sininger and Oba, 2001). The stimuli used for ABR testing are of different types. Clicks are broadband stimuli that are particularly good for eliciting an ABR because they excite many cochlear elements and neurons almost simultaneously. ABR thresholds determined using click stimuli correspond closely to the average hearing levels of an audiogram (Sininger and Abdala, 1998). Frequency-specific tone bursts (short-duration tones created with slow rising onset and offset ramps) are the best ABR stimuli for the purpose of determining the degree and configuration of hearing loss and for predicting the specific thresholds on an audiogram. Figure 3-2 shows a typical ABR
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Hearing Loss: Determining Eligibility for Social Security Benefits FIGURE 3-2 Infant auditory brainstem response to 4000 Hz tone burst. intensity series recorded from an infant with normal hearing in response to 4000 Hz tone bursts. Generally, tone bursts in the frequency range between 500 and 4000 Hz provide adequate information for accurate prediction of the hearing thresholds in subjects of any age. Subjects must cooperate for the ABR evaluation by reclining and remaining nearly motionless in a darkened, sound-treated room during the test. Infants generally are tested during natural sleep; toddlers may need mild sedation for a competent evaluation. Older children and adults are tested in a quiet dark environment while reclined and are encouraged to sleep during the evaluation. The test requires that a minimum of three electrodes be attached to the scalp after mild skin abrasion for adequate connection. The subject is asked to wear headphones or use foam insert plugs connected to transducers. A full evaluation may take 15 minutes to 2 hours, depending on results and degree of cooperation. ABRs can be
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Hearing Loss: Determining Eligibility for Social Security Benefits elicited with bone-conducted stimuli when needed for differential diagnosis of conductive hearing loss or evaluation of ears with closed ear canals (Lasky and Yang, 1986; Stuart, Yang, and Green, 1994; Yang and Stuart, 1990; Yang, Rupert, and Moushegian, 1987). The auditory steady-state response (ASSR), previously known as the steady-state evoked potential (SSEP), is another way of objectively assessing frequency-specific responses. In simple terms, this technique uses pure-tone (carrier) stimuli that are modulated at an appropriate amplitude with another tone at an appropriate modulation frequency. For infants and children, the appropriate modulation frequency range is about 80-100 Hz. Long segments of these stimuli are presented and ongoing electroencephalographic activity is sampled and analyzed in the frequency domain. When the neural activity shows a preference for the modulation frequency over other frequencies in the analysis, it is assumed that the auditory system is responding to the carrier frequency. A response is determined statistically by highly coherent phase in repeated measurements at the target frequency, or by significantly greater amplitude of modulation spectral components than surrounding frequencies, or both. ASSR detection is completely automated. In addition, it can be quite fast as a clinical measure. Picton has shown (Picton et al., 1998), by using a variety of modulation frequencies, that up to four stimuli can be tested in each ear simultaneously. This technique has been shown to be of value in assessing aided hearing thresholds in the sound field (Picton et al., 1998). Hearing thresholds have been estimated to be within about 10-15 dB of thresholds obtained by standard audiometric techniques in adults with normal hearing and hearing loss using the multifrequency ASSR (Dimitrijevic et al., 2002). One reservation about the use of ASSR for measurement of hearing is the lack of good data on infants and children (Stapells et al., 1995). Rickards et al. (1994) have found that normally hearing infants may not have a reliable response below about 40 dB. This would make it impossible to distinguish between mild hearing loss and normal hearing, a distinction that is critically important for determination of amplification needs. Perez-Abalo and colleagues (2001) have shown that, although they were able to determine hearing loss in the severe and profound range, in general, there was only fair agreement between ASSR thresholds and hearing levels in children with hearing loss. Her data also show that ASSR was unable to determine hearing levels below 40 to 50 dB nHL in the children at any frequency. At this time it would be not be prudent to recommend the use of ASSR to determine hearing loss in infants and young children, especially those with mild and moderate hearing loss.
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Hearing Loss: Determining Eligibility for Social Security Benefits Assessment When Exaggerated Hearing Loss Is Suspected On occasion, an individual may feign a hearing loss or exaggerate one during routine audiometric assessment for financial compensation, to gain attention, or to acquire some form of special treatment. The terms “pseudohypacusis” and “malingering” may be used to describe these cases. Pseudohypacusis refers to a hearing loss without an organic basis; malingering describes cases of willful simulation of a hearing loss. Regardless of the motivation for pseudohypacusis, the audiologist’s responsibilities are to determine whether an individual is providing accurate thresholds and, if not, to estimate the true audiometric thresholds. Some behavioral signs of pseudohypacusis include exaggerated behavior during a case history interview or report of a hearing loss that is inconsistent with an individual’s apparent communication ability. Routine pure-tone and speech audiometry often reveal inconsistencies that are indicative of pseudohypacusis: poor agreement between repeated thresholds measured at one frequency (> 5 dB), poor agreement between average pure-tone thresholds and the speech recognition thresholds (> 6 dB), exaggerated inconsistency between average pure-tone thresholds measured with a descending procedure and speech recognition thresholds measured with an ascending procedure (> 10 dB) (Schlauch, Arnce, Olson, Sanchez, and Doyle, 1996), absence of a “shadow” threshold curve in the poorer ear in cases of a profound unilateral hearing loss, excellent speech recognition scores at relatively low presentation levels (20 dB above admitted threshold), and no response to unmasked bone conduction stimuli with bone conduction oscillator placement on the poorer ear. In addition, acoustic reflex thresholds may be elicited at levels that are lower (better) than admitted behavioral pure-tone thresholds, confirming the presence of pseudohypacusis. Pseudohypacusis frequently is resolved with reinstruction and repeated assessment of pure-tone thresholds using an ascending technique on the same day or on another day. Other behavioral techniques that can be used to estimate pure-tone thresholds with reasonable accuracy and without the need for special equipment are the Stenger test for cases of unilateral hearing loss (Newby, 1964) and the Sensorineural Acuity Level (SAL) test (Rintelmann and Harford, 1963). A simple technique is to count pulses of variable intensity (Ross, 1964), that is, to ask listeners to count a series of beeps. This technique is particularly useful for children. For individuals whose exaggerated auditory thresholds do not resolve with these or other special behavioral techniques (e.g., Bekesy tracking, Jerger and Herer, 1961; delayed auditory feedback, Ruhm and Cooper, 1964), the ABR is the technique that will be chosen by most audiologists in the United States to estimate hearing sensitivity. Cortical
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Hearing Loss: Determining Eligibility for Social Security Benefits evoked potentials, also known as late potentials, can also be used successfully in the objective assessment of hearing for adults (Coles and Mason, 1984; Hone et al., 2003; Hyde et al., 1986; Tsui et al., 2002). A discussion of techniques for management of pseudohypacusis can be found in a review chapter by Snyder (2001). Multiple Conditions Patients may present with a variety of disabling conditions, in addition to the hearing loss, that may interfere with routine testing procedures. For example, a severe neurological or motor problem that prevents an individual from providing a time-locked behavioral response requires modification of the standard paradigm in order to obtain an accurate measure of threshold. Any behavioral response that is under the listener’s control may be used to signify signal detection, such as a finger motion, an eyeblink, or a directed eye gaze. Loss of visual acuity as the sole additional disabling condition generally has no effect on routine audiometric assessment procedures. However, this condition would negatively impact performance on measures that combine auditory and visual presentation of stimuli. Individuals with mental retardation or developmental disabilities may have difficulty responding to abstract pure-tone signals with a standard behavioral response. Techniques used for children of an equivalent developmental age may be applied with these persons. When modified procedures do not produce reliable thresholds (pure tone or speech) or suprathreshold speech recognition scores, then assessment with electrophysiological techniques such as ABR is often utilized.
Representative terms from entire chapter: