Safety of Interferon Alpha-2a in Patients with Severe Ophthalmic Behçet's Disease: Response to Bielefeld et al.'s Letter.

Thyroid dysfunction is a common and severe side-effect encountered in up to 40% of patients treated with IFN-alpha-2a. The main two mechanisms by which IFN-alpha-2a induces thyroid dysfunction can be categorized as autoimmune and non-autoimmune disease. In the first subgroup, thyroid antibodies are found before treatment initiation, and then patients develop thyroiditis. In the second subgroup, IFN-alpha-2a induces thyroiditis by a direct cytotoxic effect on the thyroid gland; in this case, thyroid antibodies are usually negative. To avoid such complications, patients should undergo routine thyroid screening (thyroid-stimulating hormone and thyroid antibodies) prior to IFN-alpha-2a initiation, during the treatment period, and 6 months after treatment withdrawal.