Treatment with interferon beta does not appear to affect progression to disability in patients with relapsing-remitting multiple sclerosis (MS), according to a new study.
Researchers performed a retrospective cohort study of 1995-2008 data from patients in British Columbia, Canada, to determine the relationship between interferon beta, a common MS treatment, and disability progression. Patients who had relapsing-remitting MS and were treated with interferon beta (n=868) were compared with a contemporary cohort eligible for treatment by the study criteria who were not exposed to interferon beta (n=829) and a historical cohort who would have been eligible for treatment by the study criteria before interferon beta was available in Canada (n=959). The study's main outcome measure was the time from baseline, defined as the point of eligibility for interferon beta treatment, to a confirmed, sustained score of 6 on the Expanded Disability Status Scale (EDSS). The EDSS ranges from 0 to 10; higher scores indicate greater disability. A person with a score of 6 requires a cane, crutch or brace to walk 100 meters. The study also looked at the association between interferon beta treatment and the hazard of disease progression. Results appeared in the July 18 Journal of the American Medical Association.
The median active follow-up times, from first to last EDSS measurement, were 5.1 years for the interferon beta cohort, 4.0 years for the contemporary cohort, and 10.8 years for the historical cohort. Overall, 10.8%, 5.3% and 23.1% of patients in each cohort, respectively, reached a sustained EDSS score of 6. The authors adjusted for sex, age, disease duration and EDSS score and found no association between interferon beta treatment and a statistically significant difference in reaching an EDSS score of 6 (hazard ratios, 1.30 compared with the contemporary cohort and 0.77 compared with the historical cohort; P=0.14 and 0.07, respectively). These results did not change after additional adjustment for comorbid conditions and socioeconomic status or after propensity score adjustment.
The authors noted that they were not able to test different types of interferon beta drugs separately and did not take adverse events of treatment into account, among other study limitations. However, they concluded that in patients with relapsing-remitting MS, interferon beta does not appear to slow progression to disability, which they called the “ultimate goal” of MS treatment. Their findings question whether interferon beta should be used routinely for this indication, they wrote, although they stressed that the treatment may still benefit an as-yet-identified subset of patients.
An accompanying editorial called the study an important contribution to the literature but pointed out that “Lacking evidence of treatment effect is not proof of lacking effect.” The editorialists noted that the study may have been underpowered and that the results could be biased against interferon because a significant proportion of the contemporary cohort may have had disease mild enough to disqualify them from treatment consideration.
The editorialists said that neurologists will probably continue to prescribe interferon beta for relapsing-remitting MS based on existing evidence pointing to short-term benefits. “However, the rigorously collected data [in the current study] reinforce the conclusion that the associations between use of interferons and long-term disability, although plausible, remain unproven,” the editorialists wrote.