Intramuscular interferon beta-1a therapy initiated during a first demyelinating event in multiple sclerosis.

Background: Treatment with interferon beta has been shown to help patients with established multiple sclerosis, but it is not known whether initiating treatment at the time of a first clinical demyelinating event is of value. Methods: We conducted a randomized, double-blind trial of 383 patients who had a first acute clinical demyelinating event (optic neuritis, incomplete transverse myelitis, or a brain-stem or cerebellar syndrome) and evidence of prior subclinical demyelination on magnetic resonance imaging (MRI) of the brain. After initial treatment with corticosteroids, 193 patients were randomly assigned to receive weekly intramuscular injections of 30 microg of interferon beta-1a and 190 were assigned to receive weekly injections of placebo. The study end points were the development of clinically definite multiple sclerosis and changes in findings on MRI of the brain. The trial was stopped after a preplanned interim efficacy analysis. Results: During three years of follow-up, the cumulative probability of the development of clinically definite multiple sclerosis was significantly lower in the interferon beta-1a group than in the placebo group (rate ratio, 0.56; 95 percent confidence interval, 0.38 to 0.81; P = 0.002). As compared with the patients in the placebo group, patients in the interferon beta-1a group had a relative reduction in the volume of brain lesions (P<0.001), fewer new or enlarging lesions (P<0.001), and fewer gadolinium-enhancing lesions (P<0.001) at 18 months. Conclusions: Initiating treatment with interferon beta-1a at the time of a first demyelinating event is beneficial for patients with brain lesions on MRI that indicate a high risk of clinically definite multiple sclerosis. (N Engl J Med 2000;343:898-904.) (C)2000, Massachusetts Medical Society.