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Long-Term Follow-Up of 106 Multiple Sclerosis Patients Undergoing Interferon-ß 1a or 1b Therapy: Predictive Factors of Thyroid Disease Development and Duration

Departments of Internal Medicine (N.C., A.D., E.F., F.Mo.) and Neuroscience (F.Ma., L.Ma., L.P., A.I., L.Mu.), University of Pisa, 56126 Pisa, Italy

Address all correspondence and requests for reprints to: Fabio Monzani, M.D., Department of Internal Medicine, University of Pisa, via Roma 67, 56126 Pisa, Italy. E-mail: fmonzani{at}med.unipi.it.

Background: Conflicting data have been reported on the association between interferon (IFN)-ß therapy of multiple sclerosis (MS) patients and thyroid disease development.

Aims: The goals of this study are as follows: to assess the actual occurrence of thyroid dysfunction and autoimmunity during long-term IFN-ß therapy; to establish the possible presence of predictive factors for thyroid dysfunction development and duration; and to suggest an effective follow-up protocol for patients receiving long-term IFN-ß therapy.

Study Protocol: A total of 106 MS patients (76 women) underwent IFN-ß 1a or 1b therapy for up to 84 months (median, 42 months). Thyroid function and autoimmunity were assessed at baseline and every 3–6 months throughout the treatment course.

Results: Baseline thyroid autoimmunity was detected in 8.5% of patients and hypothyroidism in 2.8%. Thyroid dysfunction (80% hypothyroidism, 92% subclinical, 56% transient) developed in 24% (68% with autoimmunity) of patients and autoimmunity in 22.7% (45.5% with dysfunction), without significant differences between the two cytokines; 68% of dysfunctions occurred within the first year. Autoimmunity emerged as the only predictive factor for dysfunction development (relative risk, 8.9), whereas sustained disease was significantly associated with male gender (P < 0.003).

Conclusions: Both incident thyroid autoimmunity and dysfunction frequently occur in MS patients during IFN-ß therapy, particularly within the first year of treatment. Thyroid dysfunction is generally subclinical and transient in over than half of cases; preexisting or incident autoimmunity emerged as the only significant predictive factor for thyroid dysfunction development. Thyroid function and autoimmunity assessment is mandatory within the first year of IFN-ß therapy; thereafter, serum TSH measurement only in patients with thyroid disease could be sufficient.

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