The accuracy of prevalence rates of multiple sclerosis: a critical review.

Review of the recent medical literature raises doubts about the reliability of reported prevalence rates of multiple sclerosis (MS). Many published prevalence rates are inflated. Some studies have shown that relying on clinical information and MRI interpretation leads to one third of incorrect MS diagnoses. The most important error is failing to distinguish between the clinical and MRI characteristics of MS and of disseminated encephalomyelitis (DEM) in both their acute and relapsing forms. The diagnostic criteria in current usage, including those relating to imaging, do not differentiate between MS and other recurrent inflammatory demyelinating diseases of the central nervous system. Considering a second demyelinating episode following a clinically isolated symptom or acute DEM, as confirming MS, is another major source of error. Another is including cases with onset before they entered the study group or moved to the geographic area. Neuromyelitis optica (NMO) has long been considered an MS variant and in Far Eastern countries it is counted as the 'oriental' form of MS, falsely inflating prevalence rates of MS in those areas. Recent immunologic and radiologic evidence shows that at least some NMO cases represent instances of DEM.