or laboratory tests, but also from the nature of the symptoms themselves. The symptoms are nonspecific and common, both in the community (Kroenke and Price, 1993) and in primary care (Kroenke et al., 1994). About 33 percent of patients in primary care, for instance, complain of four or more common symptoms (Kroenke et al., 1994). With nonspecific, common symptoms and no objective abnormalities, researchers have few guarantees that they are studying a homogeneous patient population. If the population is heterogeneous, this obscures researchers’ ability to detect differences between those with the index condition and those without. This is referred to as the problem of specificity, and it plagues research on medically unexplained illnesses (Hyams, 1998). What is now grouped together as “unexplained illnesses” in Gulf War veterans, for example, might comprise heterogeneous illnesses with different etiologies, pathogenesis, and risk factors.

One potential solution to the problem of specificity is to take a dimensional, rather than a categorical, approach to identifying cases (Wessely et al., 1999). These and other investigators argue that the symptom overlap across medically unexplained illnesses13 is so great that the differences represent an artifact of medical specialization or semantics (Clauw and Chrousos, 1997; Wessely et al.,


The hallmarks of fibromyalgia are widespread muscle pain and tenderness upon palpation at numerous preestablished soft tissue sites on the body, according to classification criteria promulgated by the American College of Rheumatology (Wolfe et al., 1990). The formulation of criteria was a watershed event in the evolution of a condition that had been described for more than a century and given various labels, the most recent of which was fibrositis. Other common symptoms entail fatigue, sleep disturbance, morning stiffness, and cognitive impairment, but these are not sensitive and specific enough to use for classification (Wolfe et al., 1990). Early characterizations of the condition as an inflammation of muscle (hence the label fibrositis) have not been borne out through research (Goldenberg, 1999). There is no pathological or laboratory test with which to confirm the diagnosis. Nor is there any widely accepted etiology. Fibromyalgia’s prevalence is about 2 percent of the population, making it one of the more common rheumatological disorders (Wolfe et al., 1995). Fibromyalgia is 10 times more common in females, and its occurrence increases with age (Wolfe et al., 1995). On the basis of longitudinal studies, the course is chronic, yet variable in intensity (Wolfe et al., 1997). Several types of treatment have been found to be effective in controlled trials, including the tricyclic antidepressant amitriptyline, alone or in combination with fluoxetine (Prozac), as well as cognitive behavioral therapy and exercise. Anti-inflammatory and analgesic medications are no more effective than placebo (Goldenberg, 1999).


Their lists of medically unexplained illnesses do not include illnesses in Gulf War veterans (Clauw and Chrousos, 1998; Wessely et al., 1999).

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