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The Lack of Nocturnal Serum Thyrotropin Surge in Patients with Nontoxic Nodular Goiter May Predict the Subsequent Occurrence of Hyperthyroidism^*

Istituto di Endocrinologia, University of Pisa Pisa
Cattedra di Endocrinologia, University of Cagliari Cagliari, Italy

Address requests for reprints to: Dr. Luigi Bartalena, Cattedra di Endocrinologia e Medicina Costituzionale, University of Pisa, Viale del Tirreno 64, 56018 Tirrenia, Pisa, Italy.

TSH secretion, with particular regard to the nocturnal TSH surge, was evaluated in 115 subjects with nontoxic nodular goiter. All patients were clinically and biochemically euthyroid. After 18–36 months of follow-up (mean, 24 months), hyperthyroidism occurred in 21 (18%; group 1), while the remaining 94 remained euthyroid (82%; group II). The analysis of hormonal data at the time of first observation showed that the 2 groups had similar total and free T₄ and T₃ serum concentrations. Morning serum TSH values in group I were lower than those in group II patients (0.6 ± 0.1 vs. 1.1 ± 0.1 mU/L; P < 0.001); this difference was even more striking for the nocturnal values (0.6 ± 0.1 vs. 2.2 ± 0.2 mU/L; P < 0.0001); nocturnal values were significantly lower than morning values in group II, but not in group I. The mean peak TSH value after TRH was also significantly reduced in group I (5.5 ± 0.4 us. 9.2 ± 0.7 mU/L; P < 0.001). Morning TSH values in group II did not differ from those in controls (1.3 ± 0.1 mU/L), whereas nocturnal and TRH-stimulated peak TSH values were slightly but significantly lower. The nocturnal serum TSH values in control subjects were 62–390% higher than morning values. The nocturnal TSH surge was abolished in 18 of 21 (86%) group I patients and in 7 of 94 (8%) group II patients. TRH testing resulted in an absent or blunted TSH response in 5 subjects in group I and 6 in group II. Analysis by the Galen and Gambino predictive model, comparing the abolition of the nocturnal TSH surge and the abnormal TRH test as predictors of the subsequent occurrence of hyperthyroidism, showed that the former had higher sensitivity (86% vs. 24%) and predictivity (72% vs. 45%). In conclusion, the results of the present study demonstrate that the evaluation of the nocturnal TSH surge may be useful in identifying patients with nontoxic nodular goiter in whom hyperthyroidism may eventually occur. Patients who lack the nocturnal serum TSH surge are more prone to develop thyroid hyperfunction; their thyroid status should, therefore, be more carefully and frequently monitored.

^* This work was supported in part by grants from the Ministero della Pubblica Istruzione (60%; Rome, Italy) and the Assessorato Difesa Ambiente, Regione Autonoma Sardegna, Italy.

Received July 30, 1990.

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