Benign multiple sclerosis in Crete

Our objective was to study multiple sclerosis on Crete, an island of 0.6 million inhabitants sharing a similar genetic background and the same environment. Case ascertainment was achieved using the MS Epidemiology Program Project of Crete. The diagnosis and classification of multiple sclerosis were made by established clinical and magnetic resonance imaging criteria, and disease evolution was assessed by periodic evaluations. Thorough clinical and laboratory evaluations were conducted; a detailed history, including a questionnaire of 36 items, was taken. Data obtained were analysed for possible interaction with disease prognosis. We identified 587 cases of multiple sclerosis (F:M = 1.6), >90% of which were of Cretan origin from both parental lines. Age at onset was 31.5 +/- 10.3 years (mean +/- SD) and disease duration 12.7 +/- 9.1 years. About 84.6% had relapsing remitting multiple sclerosis, 9.4% primary progressive multiple sclerosis and 6% clinically isolated syndrome. Nearly 40% of our multiple sclerosis patients with disease duration >10 years (mean = 16.2 +/- 5.3 years) remained with no or mild disability (Expanded Disability Status Scale [EDSS] <= 3). Also, about 30% of patients with relapsing remitting multiple sclerosis showed benign disease evolution (EDSS <= 3) more than 20 years (mean = 24.0 +/- 3.3) after onset. Factors predisposing to benign multiple sclerosis included younger age at onset, shorter disease duration and a lower number of relapses. We conclude that a substantial proportion of patients with multiple sclerosis from Crete follow a rather benign disease course, and this may relate to the genetic background of the population and/or to environmental factors.