Suspected Thymoma as the Initial Presentation of Graves' Disease: A Report of a Rare Case and Comprehensive Literature Review.

Graves' disease (GD) is an autoimmune endocrinopathy characterized by thyrotropin receptor-stimulating antibodies that lead to hyperthyroidism. In addition to thyroid dysfunction, patients with GD may develop extrathyroidal manifestations, including thymic hyperplasia (TH), which often presents as an incidental anterior mediastinal mass that typically regresses with treatment of hyperthyroidism. In contrast, a thymoma is a rare thymic epithelial tumor that may present with similar imaging findings but requires distinct diagnostic and therapeutic management. The coexistence of GD and thymoma is exceedingly rare. This report describes the case of a 35-year-old female patient with newly diagnosed GD who was incidentally found to have an anterior mediastinal mass. Imaging and subsequent percutaneous biopsy were highly suspicious for thymoma, illustrating the diagnostic challenge of distinguishing TH from thymoma in patients with GD. This case underscores the importance of maintaining a broad differential for persistent thymic enlargement in hyperthyroidism, ensuring neoplastic masses are not misattributed to benign TH.