Drug abuse as a risk factor of multiple sclerosis: case-control analysis and a study of heterogeneity.

The etiology of multiple sclerosis (MS) remains unknown despite considerable research involving a number of disciplines for many decades. Cluster analysis was used to disentangle the possible heterogeneity of MS, based on clinical characteristics of 108 subjects. Further on, a case-control study was conducted within each subgroup found with the cluster analysis, to test with more validity environmental risk factors, such as alcohol, tobacco, medication and drug abuse. The controls with a rheumatoid arthritis condition were matched to the cases on age, gender and same postdiagnostic period and were recruited from the same hospital. Three main groups of MS subjects were obtained from the cluster analysis, distinguished by the gender, the presence or not of family history and the degree of severity of their physical disability. The results showed that drug abuse was the only risk factor with a statistically significant odds ratio for overall and for the unique female group without familial history of MS.