Central Hypothyroidism Related to Pituitary Adenomas: Low Incidence of Central Hypothyroidism in Patients With Acromegaly

Context: The most frequent cause of central hypothyroidism (CeH) is pituitary adenomas, but the mechanisms remain unclear. Objective: We investigated serum thyroid levels and GH/IGF-1 in central hypothyroidism in untreated patients with pituitary nonfunctioning and GH-secreting adenomas. Design: This was a retrospective cross-sectional study of cases collected from Gunma University and Toranomon Hospitals between 2007 and 2016. Patients: One-hundred thirty-nine cases of nonfunctioning pituitary adenoma (NFPA) and 150 cases of GH-secreting pituitary adenoma (GHPA) were analyzed. Main Outcome Measures: The correlations between thyroid levels, several clinicopathological parameters, and GH/IGF-1 were examined. Results: Twenty-four percent of NFPA patients had CeH. The severity did not correlate with tumor size, age, or sex, and all cases had normal TSH levels. In contrast, only 8.7% of GHPA patients had CeH; approximately half had normal TSH levels and approximately half had low TSH levels. Serum TSH levels in GHPA patients were significantly lower and free T4 (FT4) and free T3 levels were higher than those in patients with NFPA. Furthermore, approximately one-fourth of GHPA patients had normal FT4 and low TSH levels. In addition, serum FT4 levels and serum TSH levels were positively and negatively correlated, respectively, with serum IGF-1 levels. Furthermore, IGF-1 levels in patients with GHPA decreased with age. Conclusions: (i) NFPA patients with CeH had TSH levels within a normal range. (ii) GHPA patients had a low incidence of CeH, which may be a result of stimulated thyroid function by GH/IGF-1. (iii) We found an age-dependent decrease in serum IGF-1 levels in patients with GHPA.