DECREASE IN THYROID HORMONES SECRETED BY TOXIC NODULAR GOITER FOLLOWING A DECLINE OF INSULIN-LIKE GROWTH FACTOR-I AND GROWTH HORMONE LEVELS IN AN ACROMEGALIC CASE.

Sustained exposure to high serum insulin-like growth factor (IGF-1) levels is likely to play a role in the development of the thyroid tumor in acromegaly; however,there is no report that indicate a promoting effect on the secretion of hormones by the thyroid tumor. We report a case of acromegaly in a seventy-one-year-old female with primary subclinical hyperthyroidism. Autoantibodies including anti-thyroglobulin antibody, anti-thyroid peroxidase antibody and thyroid stimulating hormone (TSH) receptor antibody were all negative. Ultrasonography of the thyroid demonstrated a solid adenoma in the left thyroid lobe and Technetium-99m thyroid scintigraphy showed a high level of accumulation into the same lesion, indicating that toxic nodular goiter (TNG) was the cause of hyperthyroidism. Despite serum thyroid hormones remaining at normal levels, serum TSH levels went on decreasing gradually until transsphenoidal surgery to treat a growth hormone (GH) secreting pituitary adenoma. Interestingly, as IGF-I and GH levels normalized after operation, the serum TSH level increased and finally reached the normal level without intervention to the thyroid. Additionally, accumulation of Technetium-99m seen with thyroid scintigraphy slightly decreased. The evidence obtained from this case may suggest a novel mechanism whereby excessive secretion of thyroid hormones from TNG in an acromegalic patient is regulated by IGF-I. [ABSTRACT FROM AUTHOR]