A CASE OF AN AUTONOMOUSLY FUNCTIONING THYROID NODULE ASSOCIATED WITH LOW TRIIODOTHYRONINE CONCENTRATIONS

Abstract

A 66-year-old woman with an autonomously functioning thyroid nodule (AFTN) showed low serum levels of triiodothyronine (T₃) and no response of thyroid stimulating hormone (TSH) to thyrotropin releasing hormone (TRH). After administration of methimazole, TSH level increased from 0.1 to 19μ/U/ml. After surgical removal of the thyroid nodule, both TSH and T₃ levels increased to normal and the response of TSH to TRH stimulation became normal. These findings suggest that the AFTN may be associated with low T₃ concentrations and that certain substances released by the AFTN may be responsible for the inhibition of pituitary TSH response to TRH stimulation.