Preclinical hyperthyroidism in multinodular goiter.

The thyrotropin (TSH) response to thyrotropin-releasing hormone(TRH) (200 mug iv) was determined in 80 surgical patients with nontoxic multinodular goiter. The TSH reserve was normal in multinodular goiter. The TSH reserve was normal in 55 and elavated in 8 patients. No TSH response to TRH (deltaTSH less than or equal to 1 muU/ml) was detectable in 17 patients (21%). Individual and mean serum T4, FT4I and serum T3 values did not differ from normal in 13 of the TRH unresponsive patients; in 4 patients FT4I or serum T3 was marginally elevated. No statistical differences were noted for I131-uptake, PBI131 and conversion rate between controls and TRH unresponsive patients. All patients who failed to respond to TRH were euthyroid on clinical evaluation. Goiters were large multinodular and long-standing in most instances. In 12 tested subjects TRH responsiveness recovered following partial thyroidectomy. In 3 of 7 TRH unresponsive euthyroid patients tested 9-12 days post surgery a transient lack of TSH to respond to TRH was observed. Recovery of TRH responsiveness was accompanied by a significant (P IS LESS THAN 0, 02) decrease in serum T4and FT4I in the euthyroid range, whereas no change in serum T3 occurred. It is suggested that TRH unresponsiveness represents a state of preclinical hyperthyroidism maintained by autonomously functioning goiter compartments.