Transient Lack of Thyrotropin (TSH) Response to Thyrotropin-Releasing Hormone (TRH) in Treated Hyperthyroid Patients with Normal or Low Serum Thyroxine (T4) and Triiodothyronine (T3)1

Abstract

Stimulation with TRH has been carried out in 6 patients with hyperfunctioning autonomous adenoma and 1 patient with toxic multinodular goiter, before and at different intervals after surgery of the thyroid. Serum TSH, T₄ and T₃ were determined by radioimmunoassay. Before treatment, the serum TSH was undetectable in all patients, both prior to and during the TRH test. The same pattern was found for several weeks after ablation of the adenoma and/or part of the thyroid, though serum T₄ and T₃ levels were normal or definitely lower than normal. This situation was transient, and later the serum TSH levels became higher than normal and responsiveness to TRH was observed. For most of the patients studied this occurred with serum T₄ and T₃ levels which were higher than during the period when serum TSH was undetectable.