Persistent anterior mediastinal mass in a patient with Graves' disease

Graves' disease is an autoimmune disease that affects 0.5 per cent of the population and is the etiology of hyperthyroidism in 50 to 80 per cent of cases.1 These patients present with weight loss, heat intolerance, tremor, proximal muscle weakness, and proptosis as a result of elevated IgG antibodies that activate the G-coupled thyrotropin receptor.1 Graves' disease has been linked to associated thymic hyperplasia and was originally described by Halsted et al. in the early 20th century.2 Thymic hyperplasia has been characterized into two distinct forms:3 1 true hyperplasia that is delineated by hypertrophy of the gland with normal cortical and medullary thymic parenchyma; and 2 thymic lymphoid hyperplasia in which there is an increase in the lymphoid follicles and germinal centers with minimal gland enlargement.