Massive Thymic Hyperplasia Secondary to Graves Disease

ABSTRACT Objective Graves disease (GD) has a well-known association with thymic hyperplasia, which is seen histo-logically in up to 38% of patients with GD. However, there have only been approximately 100 documented cases of Graves-associated massive thymic hyperplasia. Potential mechanisms of thymic pathology are reviewed. Methods A 24-year-old female presented to the emergency department with dyspnea, palpitations, tachycardia, anxiety, and weight loss. She was evaluated for hyperthyroidism using labs (thyroid-stimulating hormone, free thyroxine, thyroid-stimulating immunoglobulins) and imaging (radioactive iodine uptake [RAIU] scan), leading to treatment with radioiodine. A computed tomography angiogram of the chest was also performed to evaluate for pulmonary embolism given the patient's presenting symptoms. Results Our patient was found to have undetectable thyroid-stimulating hormone, elevated free thyroxine (2.9 ng/dL), and elevated thyroid-stimulating immunoglobulins (399%). Diagnosis of GD was confirmed on RAIU scan. The computed tomography chest angiogram demonstrated a significant anterior mediastinal mass (7.9 × 6.9 × 6.3 cm). Treatment with radioiodine led to reduction of the mass by 76% in volume. Conclusion While the patient's thyroid labs and RAIU scan were consistent with GD, the presence of massive thymic hyperplasia was atypical. However, the resolution of thymic hyperplasia after radioiodine therapy, without the use of thymectomy, was similar to other reported cases.