Graves' disease following subacute thyroiditis.

Subacute thyroiditis is a painful, inflammatory disease frequently accompanied with fever. It is suspected to be a viral infectious disease, while Graves' disease is an autoimmune disease. Thus, there appears to be no etiological relationship between the two diseases. A total of 25,267 thyroid disease patients made their first visits to our thyroid clinic during a period of 24 years between 1985 and 2008. Among them, subacute thyroiditis and Graves' disease accounted for 918 patients (3.6%) and 4,617 patients (18.2%), respectively. We have encountered 7 patients (one male and six female) with subacute thyroiditis followed by Graves' disease in this period (0.15% of the 4,617 patients with Graves' disease and 0.76% of the 918 patients with subacute thyroiditis). The age ranges were 40~66 years (mean 48.7 years) at the onset of subacute thyroiditis. The intervals between the onsets of subacute thyroiditis and Graves' disease were 1~8 months (mean 4.7 months). Because Graves' disease was preceded by subacute thyroiditis, the signs and symptoms of both diseases were evident together in the intervening period. The diagnosis of Graves' disease in those patients is always difficult because of atypical signs and symptoms and an unclear onset time. The causes of the Graves'disease that followed subacute thyroiditis are still unknown. However, the inflammatory nature of subacute thyroiditis may lead to the activation of the autoimmune response in susceptible subjects, resulting in the onset of Graves' disease. Graves' disease should be suspected when a high blood level of thyroid hormone persists after subacute thyroiditis.