Walsh & Hoyt: Epidemiology

Epidemiologic studies of MS must now be interpreted in the context of the recent development of new diagnostic criteria. In the past, such studies were limited by a number of methodologic difficulties. In the first place, whereas diagnostic criteria for MS have been refined over time, the clinical diagnosis of MS has sometimes provoked disagreement, even among experienced neurologists. Before the development of the McDonald Criteria, there was considerable debate regarding whether or not the results of various MR imaging studies or laboratory tests (i.e., lumbar puncture) should be considered in making the diagnosis. In theory, diagnosis by postmortem pathologic examination should be accurate, but in practice, death certificates often are incomplete and underestimate the number of cases of MS. Furthermore, autopsy studies sometimes reveal the pathologic changes of MS in brains of patients who were neurologically asymptomatic during life. Because MS may not become manifest until age 50 or over, many cases may not have developed at the time of a single survey. Thus, when comparing surveys of different populations, the prevalence rate must be age-standardized.