triiodothyronine--reverse and Cushing-Syndrome

It is well known that an excess of glucocorticoids affects thyroid tests. The effect of adrenal deficiency on thyroid hormones is less well defined. We here describe the case of a 33-year-old woman with Cushing's disease who was cured by trans-sphenoidal surgery. During the postoperative period, a secondary adrenal insufficiency developed. The thyroid blood tests then revealed elevated L-triiodothyronine (T3) levels and a decrease in reverse T3. These findings suggest that secondary adrenal deficiency may be associated with high T3 levels, which may be due to an increase in the peripheral conversion of thyroxine (T4) to T3.

Topics: Adrenal Insufficiency; Adult; Cushing Syndrome; Female; Humans; Postoperative Complications; Thyroid Function Tests; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

In 15 untreated patients with Cushing's disease the regulation of TSH secretion and thyroid function was evaluated. The maximal increment of plasma TSH to TRH was 3.8 +/- 2.2 vs 8.7 +/- 2.9 muU/ml (patients with Cushing's disease vs controls; mean +/- SD; P less than 0.001). Free thyroxine-index was 21.8 +/- 5.2 vs 27.7 +/- 5.0 (P less than 0.001). Plasma T3 1.45 +/- 0.24 vs 1.96 +/- 0.32 nmol/l (P less than 0.001) and reverse T3 0.22 +/- 0.05 vs 0.20 +/- 0.08 nmol/l (N.S.). The maximal TSH increase in response to TRH was inversely correlated with plasma cortisol (P less than 0.05). The maximal increment of TSH to TRH and plasma T4, free T4 index and T3 are reduced in patients with Cushing's disease due to an impaired thyrotroph function. Plasma reverse T3, however, is normal which may be due to a simultaneous decrease in production and degradation.

Topics: Cushing Syndrome; Female; Humans; Hydrocortisone; Male; Thyroid Gland; Thyrotropin; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse