Ridgway EC, Weintraub BD, Cevallos JL, Rack MC, Maloof F. Suppression of pituitary TSH secretion in the patient with a hyperfunctioning thyroid nodule.
J Clin Invest 1973;
52:2783-92. [PMID:
4201265 PMCID:
PMC302546 DOI:
10.1172/jci107474]
[Citation(s) in RCA: 76] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
10 patients with a single hyperfunctioning thyroid nodule each were studied for pituitary thyrotropin (TSH) suppression. They were judged to be euthyroid on clinical grounds. The total thyroxine (T(4)D), free thyroxine (FT(4)), total triiodothyronine (T(3)D), and free triiodothyronine (FT(3)) were normal in most of the patients. Incorporation of (131)I into the hyperfunctioning thyroid nodules was not suppressed by the administration of physiological doses of T(3). Basal serum TSH concentrations were undetectable (<0.5 - 1.0 muU/ml) in all patients. The metabolic clearance of TSH in one patient before and after excision of the thyroid nodule was unchanged (40 vs. 42 ml/min) whereas the calculated production rate was undetectable before the operation (<29 mU/day) and normal after (103 mU/day). These data, in one patient, suggest that the undetectable concentration of TSH in these patients is a result of suppressed TSH secretion rather than accelerated TSH clearance. In eight patients, basal serum TSH concentrations failed to increase after the intravenous administration of 200 mug of thyrotropin-releasing hormone (TRH); minimal increases in serum TSH concentrations were observed in two patients. The suppression of TSH was evident despite "normal" concentrations of circulating thyroid hormones. The observation that normal serum concentrations of T(4)D, FT(4), T(3)D, and FT(3) may be associated with undetectable basal serum TSH concentrations and suppressed TSH response to TRH was also found in four hypothyroid patients given increasing doses of L-thyroxine and sequential TRH stimulation tests.
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