Background: Thymic hyperplasia is associated with Graves' disease, particularly in young patients. The degree of thymic transformation is minimal in most but not all patients. In the latter group radiological measurements of thyroid size and their change with treatment have rarely been reported. We present two patients with Graves' disease and relatively rapid resolution of thymic enlargement after successful treatment of their hyperthyroidism.
Summary: Three patients with thyrotoxicosis secondary to Graves' disease and marked thymic enlargement were seen at our institution during a 2-year period. On computed tomography (CT) studies their volumes were 67, 81, and 54 cm(3). Thymic hyperplasia in the setting of Graves' disease was the diagnosis of exclusion. Two of the patients returned for follow-up after successful treatment of thyrotoxicosis as requested. On repeat CT their thymic volumes had decreased by 72% and 78%, respectively. Two types of histological modifications of the thymus have been described in association with Graves' disease, namely, thymic parenchyma hyperplasia and medullary lymphoid hyperplasia. The mechanisms underlying thymic transformation in patients with Graves' hyperthyroidism are not completely elucidated, but autoimmune processes underlying Graves' disease are presumed to play a role. The clinical course of our patients is consistent with earlier literature, indicating that thymic enlargement may occur in conjunction with Graves' hyperthyroidism, and that it usually resolves as hyperthyroidism is treated, but there is little quantitative pre- and posttreatment of hyperthyroidism data.
Conclusion: Although every patient must be individually considered, it appears that thymic hyperplasia can be diagnosed in most Graves' hyperthyroid patients by considering the clinical context and appropriate radiologic studies such as CT. Raising awareness of the association of thymic hyperplasia in patients with Graves' hyperthyroidism and its resolution with the reversibility of the hyperthyroid state should prevent unnecessary thymic evaluation and surgery with its attendant risks.