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Plasma Free Triiodothyronine Response to Thyrotropin-Releasing Hormone to Predict the Remission of Graves’ Disease Treated with Antithyroid Drugs^*

First Division, Department of Medicine, Shimane Medical University Izumo, Japan

Address all correspondence and requests for reprints to: Kazumi Notsu, M.D., First Division, Department of Medicine, Shimane Medical University, 89–1 Enya-cho, Izumo 693, Japan.

The responses of both plasma TSH and free T₃ (FT₃) to TRH were examined in 31 patients with Graves’ disease who were euthyroid after treatment with antithyroid drugs, 6 patients with primary hypothyroidism, and 14 control subjects. TSH was measured 0, 15, 30, 60, 90, and 120 min and FT₃ was measured 0, 30,60,90,120,150, and 180 min after TRH injection (500 µg, iv). The increment in FT₃ above the basal level (FT₃) in normal controls ranged from 1.2–3.7 pmol/L, with a mean ± SD of 2.2 ± 0.8 pmol/L. The mean (±SD) FT₃ in patients with primary hypothyroidism was 0.3 ± 0.2 pmol/L. After the TRH test, antithyroid drugs were stopped in patients with Graves’ disease. Nine of 31 Graves’ patients relapsed within 6 months after the TRH test. The other 22 patients with Graves’ disease were followed while in remission during the observation period of up to 48 months. The mean (±SD) FT₃ were significantly lower in 9 Graves’ patients who relapsed than in those who achieved remission (0.5 ± 0.3 vs. 2.6 ± 1.1 pmol/L; P < 0.01). Eight of 9 Graves’ patients who relapsed showed lower FT₃ values than the lowest value (1.1 pmol/L) in 22 Graves’ patients in remission. Although the mean increment of TSH above the basal level (TSH) was also significantly different between the Graves’ patients who relapsed and those in remission (1.4 vs. 12.3 mU/L; P < 0.01), there was considerable overlap between the 2 groups. These findings suggest that FT₃ reflects the endocrinological recovery of the pituitary-thyroid axis and is a beneficial indicator for the termination of antithyroid drugs in Graves’ disease.

^* This work was reported in part at the 72nd Annual Meeting of The Endocrine Society, Atlanta, GA, 1990.

Received August 22, 1990.