Background Alterations in hypothalamic-pituitary function have been described in patients with incidentally discovered adrenal adenomas and have been attributed to their subtle hypercortisolemic status.
Methods To establish whether the central control of the hypothalamic-pituitary-thyroid axis is altered in these endocrine conditions, the nocturnal (10:30 pm-2:00 am) serum thyroid-stimulating hormone (TSH) surge (measured by dividing the difference between nighttime and morning TSH values by the morning TSH value and then multiplying by 100), the TSH response to thyrotropin-releasing hormone (200 μg as an intravenous bolus) and serum free thyroid hormone levels were evaluated in patients with adrenal incidentaloma (experimental group) and in normal controls (control group). Urinary free cortisol concentrations were also measured.
Results The nocturnal TSH surge was observed in the normal controls, whereas it was inhibited in the patients of the experimental group. Serum free triiodothyronine levels were similar in the two groups, whereas the TSH response to thyrotropin-releasing hormone was significantly lower in the experimental than in the control group. Urinary free cortisol levels were significantly higher in the experimental group.
Conclusion These data indicate that even conditions of slight glucocorticoid excess may exert inhibitory effects on TSH secretion, which suggests the presence of a slight central hypothyroidism in patients with adrenal incidentaloma.