Clinical characteristics of frequently recurring painless thyroiditis: contributions of higher thyroid hormone levels, younger onset, male gender, presence of thyroid autoantibody and absence of goiter to repeated recurrence.

Painless thyroiditis is characterized by transient thyrotoxicosis with complete recovery. Some patients, however, have repeated episodes of thyrotoxicosis, for which the mechanism of recurrence is not clear. We therefore studied the clinical characteristics in 8 patients with 4 or more episodes of thyrotoxicosis and 40 control patients. The age at onset was significantly earlier and the male-to-female ratio was significantly higher in the case group than the control group. The highest FT4 and FT3 levels were higher in the recurrent type. Multiple regression analysis showed contributions of higher peak FT4 level, male gender, presence of thyroid autoantibody, earlier onset, and smaller size of thyroid to repeated recurrence. Since the peak FT4 value, gender, autoantibody, age of onset and size of thyroid contribute to only 27.5% of the repeated recurrence cases, other factors such as genetic susceptibility or inflammatory tissue changes in thyroid may also be contributory. Further studies are needed to elucidate the mechanism underlying repeated recurrence.