Serum triiodothyronine (T3), thyroxine (T4), and thyrotropin (TSH) concentrations were measured throughout the illness of a patient with subacute nonsuppurative thyroiditis. In the initial hyperthyroid phase, which by history was 4–5 wk in duration, T3 was , T4 was , and TSH was normal and did not increase after thyrotropin-releasing hormone (TRH) infusion. T3 and T4 levels then fell rapidly,
... [Show full abstract] reaching values of and 25 days after the initial studies and and by day 46. Serum TSH was undetectable at 25 days, but on day 46 was 120 μU/ml, and was 162 μU/ml on day 58. T3 was given for 4 mo and then discontinued. One month later, T3 and T4 were in the normal range, but an additional month passed before TSH decreased from 60–80 μU/ml, to normal levels. These data indicate that the unphysiologic release of endogenous thyroid hormone that can occur in subacute thyroiditis suppresses TRH-induced TSH release. The elevation of TSH associated with normal T3 and T4 levels during the recovery period suggests that supranormal amounts of this hormone are required to maintain adequate thyroidal hormone release at this time. This TSH elevation can explain the often noted supranormal values for RAI uptake during the recovery period. The eventual return of the elevated TSH levels to normal indicates that, in patients with this disease, this abnormality does not imply the presence of permanent thyroid dysfunction.