The epidemiology of multiple sclerosis in Devon: a comparison of the new and old classification criteria.

OBJECTIVES To determine the prevalence of multiple sclerosis in Devon and compare the new McDonald classification guidelines with the Poser criteria currently used. METHODS All patients known to have multiple sclerosis and alive and resident within the chosen area on 1 June 2001 were included in the study. Seven sources of case ascertainment were used and each patient was classified according to both the Poser criteria and the McDonald guidelines. RESULTS The prevalence of multiple sclerosis in Devon was 118 per 100,000 (definite and probable cases, Poser criteria) in a population of 341,796, on the prevalence day. The prevalence of definite and possible cases, as classified by the new McDonald guidelines, was slightly lower at 117 per 100,000. Clinical demographics of the prevalent population were similar to those of other studies in the United Kingdom. CONCLUSIONS This is first survey to use the new recommended guidelines and compare these criteria with the Poser classification. The difficulties encountered with applying the new criteria in research are highlighted, as are the differences between the new and old criteria. This study reports one of the highest prevalences in the south of the UK, adding support for a north-south divide being a step effect rather than a latitudinal gradient.