Serum thyrotropin and thyroid hormone levels in humans receiving chronic potassium iodide.

Serum thyroxine (T4), triiodothyronine (T3) and thyrotropin (TSH) concentrations were measured in 13 patients with chronic obstructive pulmonary disease receiving saturated solution of potassium iodide (SSKI). All had a low serum T4 and a high serum TSH concentration. However, serum T3 levels were normal in eight. Recovery of normal thyroid function was observed in each of the seven patients in whom the iodide was discontinued. The same hormones were measured in four normal subjects who received 30 drops of SSKI daily for 11 weeks. An increase in serum TSH levels was preceded by a fall in serum concentrations of T4 and to some extent, T3. Upon SSKI withdrawal subsequent increases in the serum concentrations of both thyroid hormones, but particularly T3, resulted in the return of serum TSH to baseline levels. None of the subjects developed clinical hypothyroidism. It is not apparent why the normal subjects did not exhibit clinical or laboratory evidence of hypothyroidism while the patients with chronic pulmonary disease did. A younger age and the shorter duration of iodide administration in the normal subjects may have played a role.