Objectives: The examination of potential associations between Graves' disease and thyrotropin-producing pituitary adenoma (TSHoma) after treatment using octreotide, and of the expression of peroxisome proliferator-activated receptor gamma (PPAR gamma).
Design and methods: A specimen of resected TSHoma tissue from our case was immunohistochemically examined for expression of somatostatin receptor 2A (SSTR2A) and PPAR gamma. Specimens of thyroid tissue from two cases with Hashimoto's thyroiditis were immunohistochemically examined for expression of SSTR2A.
Results: Expression of SSTR2A and PPAR gamma was identified in TSHoma cells. SSTR2A was also expressed in lymphocytes that had infiltrated thyroid tissue in Hashimoto's thyroiditis. In previous reports, three of four patients with TSHoma displayed Graves' disease after tumor resection, and TSH is also known to play a major role in regulating immunomodulatory gene expression in thyrocytes.
Conclusions: Both the immunomodulatory effects of octreotide on intrathyroidal lymphocytes and rapid reductions in TSH may contribute to the onset of Graves' disease. Patients with TSHoma-associated autoimmune thyroiditis should undergo careful follow-up for development of Graves' disease after treatment. Both octreotide and the PPAR gamma receptor-activating ligands, thiazolidinediones, may be effective for patients with TSHoma.