Long-term interferon beta-1b therapy for MS - Is routine thyroid assessment always useful?

Background: The authors previously reported on the development of thyroid d ysfunction and autoimmunity during 1-year treatment of patients with MS wit h interferon-beta 1b (IFN beta-1b). Objective: To evaluate the evolution of incident thyroid disease and the possible development of more thyroid dise ase during longer term therapy. Patients: The authors studied 31 patients ( aged 34 +/- 7 years; 21 women) with relapsing-remitting MS during 3 years o f IFN beta-1b treatment. Systematic thyroid assessment was performed every 3 or 6 months, depending on the development of thyroid disease. Results: Af ter the first year of IFN beta-1b treatment, no further cases of thyroid di sease were observed. Among the six patients with early incident subclinical hypothyroidism, thyroid dysfunction persisted only in those with baseline autoimmune thyroiditis (n = 2). The three patients who developed transient hyperthyroidism remained euthyroid throughout the treatment course. A posit ive autoantibody titer was continually detected in only two out of five pat ients without baseline autoimmunity. Conclusions: The risk of thyroid disea se seems related to IFN beta-1b treatment during the first year only, parti cularly in patients with preexisting thyroiditis. Furthermore, incident thy roid dysfunction is generally transient and mild in degree. Indeed, we reco mmend a routine systematic thyroid assessment only in patients with baselin e thyroiditis. During the first year of therapy, serum thyroid-stimulating hormone measurement should suffice as first line test; a systematic thyroid assessment is only useful for those patients with incidental and persisten t dysfunction. Further studies with many patients will be necessary to conf irm our suggestions as broad clinical guidelines.