Cigarette smoking and the progression of multiple sclerosis." Brain 128(Pt 6

An increased risk of multiple sclerosis among smokers has been found in several prospective epidemiological studies. The association between smoking and progression of mul-tiple sclerosis has not been examined. We identified patients who had a first multiple sclerosis diagnosis recor-ded in the General Practice Research Database (GPRD) between January 1993 and December 2000. Their dia-gnosis and date of first symptoms were confirmed through examination of medical records. Smoking status was obtained from the computer records. To assess the asso-ciation between smoking and risk of multiple sclerosis, we conducted a case–control study nested in the GPRD. Up to 10 controls per case were randomly selected, matched on age, sex, practice, date of joining the practice and availability of smoking data. To assess the associatio