Spontaneous hypothyroidism after antithyroid treatment of hyperthyroid Graves' disease.

Out of 54 patients with hyperthyroid Graves' disease 35 remained euthyroid after treatment with antithyroid agents and have been continuously followed from 1 to 9 yr (4.85 +/- 2.55 yr, mean +/- SD). In 4 patients an exaggerated TSH response to TRH developed from 30 to 111 months after interrupting the treatment and one of them became hypothyroid 50 months (5.0 yr) thereafter. The annual incidence of subclinical hypothyroidism (exaggerated response to TRH) as calculated from the total number of observation yr was 2.5% and that of overt hypothyroidism was 0.6%. These figures are similar to those reported recently in 2 retrospective studies.