Elderly patients with suppressed serum TSH but normal free thyroid hormone levels usually have mild thyroid overactivity and are at increased risk of developing overt hyperthyroidism.

The clinical and biochemical characteristics of 15 elderly patients with low levels of thyrotrophin (TSH) (< 0.1 mU/L) but normal free tri-iodothyronine (T3) and free thyroxine (T4) (group S) were compared with 10 euthyroid subjects (group E) and 10 hyperthyroid patients (group T). Free T3 and free T4 were significantly higher (p < 0.05) in group S (6.3 +/- 0.5 and 18.6 +/- 1.0 pmol/l, respectively) than in group E (4.6 +/- 0.3, 12.6 +/- 0.6). In common with elderly hyperthyroid patients (group T), patients in group S had few signs or symptoms of thyrotoxicosis, but the Wayne score (clinical index of hyperthyroidism) was higher in group S than in euthyroid subjects (p < 0.05). Thyroid microsomal, thyroglobulin or thyrotrophin receptor antibodies were common in group T (n = 9) but not in groups S (n = 2) or E (n = 1). This suggests a low prevalence of Graves' disease in group S compared to group T. Combined thyrotrophin releasing hormone (TRH; 200 micrograms i.v.) and gonadotrophin releasing hormone (GnRH; 100 micrograms i.v.) tests were performed; no cases of low TSH due to hypopituitarism were identified in group S. During a mean of 7.9 (4-12) months of observation TSH reverted to the normal range (> 0.2 mU/L) in 7 of 15 patients in group S; thyroid hormone concentrations rose above the normal range in four, however, only two patients required treatment for hyperthyroidism.(ABSTRACT TRUNCATED AT 250 WORDS)