(1) autoimmune (often subclinical) hypothyroidism; (2) destructive thyroiditis; and (3)
Graves' hyperthyroidism.
These abnormalities can occur at any time during IFN therapy, from as early as 4 weeks until as late as 23 months after initiation,[6,9] and there is no clear difference between the three types, with a median date of onset of 17 weeks after start of IFN treatment.[10] Pooling of several studies shows that hypothyroidism seems to be more frequent than thyrotoxicosis ( Table 4 ).