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

The authors previously reported on the development of thyroid dysfunction and autoimmunity during 1-year treatment of patients with MS with interferon-beta 1b (IFN beta-1b).

To evaluate the evolution of incident thyroid disease and the possible development of more thyroid disease during longer term therapy.

The authors studied 31 patients (aged 34 +/- 7 years; 21 women) with relapsing-remitting MS during 3 years of IFN beta-1b treatment. Systematic thyroid assessment was performed every 3 or 6 months, depending on the development of thyroid disease.

After the first year of IFN beta-1b treatment, no further cases of thyroid disease 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 positive autoantibody titer was continually detected in only two out of five patients without baseline autoimmunity.

The risk of thyroid disease seems related to IFN beta-1b treatment during the first year only, particularly in patients with preexisting thyroiditis. Furthermore, incident thyroid dysfunction is generally transient and mild in degree. Indeed, we recommend a routine systematic thyroid assessment only in patients with baseline 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 persistent dysfunction. Further studies with many patients will be necessary to confirm our suggestions as broad clinical guidelines.