DECREASE IN ACROMEGALY-ASSOCIATED THYROID ENLARGEMENT AFTER NORMALIZATION OF IGF-1 LEVELS: A PROSPECTIVE OBSERVATION AND IN VITRO STUDY.

Goiter occurs at high frequency in acromegaly patients. Whether normalization of insulin-like growth factor 1 (IGF-1) levels could decrease goiter and thyroid volume remains unclear. Thyroid hormone levels and ultrasound measurements were assessed in 101 acromegaly patients, compared with 108 patients with nonfunctioning pituitary adenoma (NFPA) and 55 healthy controls. Thirty-four acromegaly patients underwent repeat evaluation 1 year post-transsphenoidal surgery. The effect of IGF-1 on thyroid cell proliferation, cell cycle, and apoptosis was evaluated in vitro. Acromegaly patients showed larger thyroid volume than those with NFPAs (18.32 mL vs. 9.91 mL; <.001) and healthy controls (18.32 mL vs. 9.63 mL; <.001). Duration of acromegaly was shown to be independently associated with thyroid volume enlargement (B = 0.259; 95% confidence interval, 0.162 to 0.357) in multivariate analysis. At follow-up, the median thyroid volume decreased from 22.74 to 17.87 mL in the cured group (n = 20; = .003), but the number of nodular goiters showed no significant change. Serum free thyroxine levels decreased from 13.76 to 10.08 pmol/L in the cured group ( = .006) but increased from 9.28 to 12.09 pmol/L in the active group ( = .013). Change in thyroid volume was significantly correlated with IGF-1 level ( = 0.37; = .029). In vitro, IGF-1 time- and dose-dependently promoted proliferation and secretory function of thyroid cells by enhancing cell cycle shift from the G1/S to G2/M phase and suppressing apoptosis. Acromegaly-associated thyroid volume increase, but not nodular goiter, could be reversed in cured acromegaly. IGF-1 time- and dose-dependently promoted the proliferation and secretory function of thyroid cells. = Cell Counting Kit-8; = free triiodothyronine; = free thyroxine; = growth hormone; = insulin-like growth factor 1; = magnetic resonance imaging; = nonfunctioning pituitary adenoma; = quantitative real-time-polymerase chain reaction; = thyroid-stimulating hormone.