Recovery of the pituitary–thyroid axis after surgical remission of thyroid-stimulating hormone-secreting pituitary adenomas

Abstract Purpose To identify factors associated with postoperative levothyroxine replacement and characterize long-term recovery of endogenous thyroid-stimulating hormone (TSH) responsiveness after surgical remission of TSH-secreting pituitary adenomas (TSHomas). Methods We retrospectively analyzed 36 patients with pathologically confirmed TSHoma who achieved early surgical remission after transsphenoidal surgery between 2006 and 2024 and maintained sustained disease control. Clinical, endocrine, tumor, and surgical characteristics were compared according to postoperative levothyroxine use. Serial combined pituitary function tests were used to assess recovery of stimulated TSH responsiveness. Results Ten patients (27.8%) required transient levothyroxine replacement, initiated a median of 36 days after surgery and continued for a median of 140 days. Larger tumor diameter was independently associated with replacement (odds ratio 26.5, P = 0.038). A diameter of 1.45 cm was the optimal exploratory cutoff (area under the curve 0.81; sensitivity 100%; specificity 53.8%). Among 31 patients with longitudinal testing, 22 (71.0%) showed recovery of TSH responsiveness when stimulated by thyrotropin-releasing hormone; the estimated median time to recovery was 2.02 years (95% confidence interval 1.64–4.04). Conclusion Postoperative impairment of endogenous TSH responsiveness after successful TSHoma surgery is often reversible but may persist for years. Larger tumors are associated with transient levothyroxine requirement, supporting long-term thyroid-axis monitoring and periodic reassessment of replacement therapy.