Association between thyroid function and serum cortisol in cortisol-producing adenoma patients

Purpose: Thyroid dysfunction has been reported in hypercortisolism. Previous findings regarding changes in thyroid function due to cortisol-producing adenoma (CPA) have been inconsistent. The study aimed to investigate the association between thyroid function and excessive cortisol secretion in patients with CPA and to explore the changes in pituitary function after adrenalectomy. Methods: We conducted a retrospective study; thyroid function was evaluated in 94 patients with CPA and 94 healthy controls (HC) matched for age and sex. A total of 94 patients with nonfunctioning adrenal incidentalomas (NFAIs) were recruited as a second control group. Results: Serum thyroid stimulating hormone (TSH) and free thyroxine (T4) levels were significantly lower in the CPA group than in the HC and NFAIs groups (P < 0.001). The prevalence of central hypothyroidism was 12.8% in the CPA group and increased according to serum cortisol quartiles (P for trend = 0.025). According to the stepwise multiple linear regression analysis, serum cortisol was negatively associated with TSH and free T4 levels in the CPA group after adjustment for body mass index and age. Furthermore, decreased TSH levels were corrected by adrenalectomy [0.75 (0.50, 1.14) vs. 1.91 (1.36, 2.71) µIU/ml, P < 0.001], in parallel with a recovery in free T4 levels [11.20 (10.00, 12.43) vs. 12.04 (11.24, 13.01), P < 0.001]. Postoperative growth hormone and prolactin levels did not change compared with baseline. Conclusion: Serum TSH and free T4 levels were decreased in patients with CPA, and dysfunction of the hypothalamic–pituitary–thyroid axis might be reversible after surgery.