Graves' Disease and Thymic Hyperplasia: The Relationship of Thymic Volume to Thyroid Function

Abstract

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.

Graves’ Disease TSHR-Stimulating Antibodies (TSAbs) Induce the Activation of Immature Thymocytes: A Clue to the Riddle of TSAbs Generation?

“…The mechanism behind thymic hyperplasia in GD has been the subject of speculation. Since the detection up to 1996 of TSHR in total thymus tissue extracts (23,34), the possibility of TSAbs being involved in the process has been repeatedly proposed (35), and a possible effect of GD IgGs on thymocytes was first experimentally demonstrated, in a single case, in 1988 (36). Our data demonstrating the functional interaction between TSAbs and thymic TSHR supports this hypothesis.…”

“…Clarifying the origin of thymic hyperplasia in GD is of general clinical interest because thymus enlargement (due to hyperplasia or thymoma) is also a common feature in myasthenia gravis, a much less common disorder. The understanding of the pathogenesis of GD-associated thymic hyperplasia will increase clinical awareness on the fact that finding thymic enlargement should not direct only to the suspicion of myasthenia, but also to GD, which, by an unrelated mechanism, also produces muscle weakness and is a much more common disorder (24,35).…”

Thymic hyperplasia in patients with Graves’ disease

“…In the light of the above hypotheses, Popoveniuc et al [35] suggested that two different pathogenic mechanisms might be involved in thymic enlargement. Thymic cortical tissue expansion seems to be due to a hyperthyroid state involving increased levels of thymulin, a protein involved in lymphocyte differentiation and function [36], whereas lymphoid hyperplasia appears to correlate with immune abnormalities underlying GD [37].…”

Enlarged Thymus in a Patient With Dyspnea and Weight Loss

“…The time to involution varies from 8 weeks (after thyroidectomy) to 4 to 25 months (after antithyroid medication). 5,10 In a recent report, 4 cases of malignancy were confirmed among 107 cases of thymic enlargement in Graves disease, including 3 cases of thymoma and 1 case of T lymphoblastic leukemia/ lymphoma. Therefore, it is reasonable to ensure involution of the thymus by repeat imaging once hyperthyroidism has been treated.…”

“…9 Treatment of Graves disease with antithyroid medications or thyroidectomy usually leads to involution of thymic hyperplasia. 3,5,7,10 With improvement of Graves disease, there is a decrease in signal density of thymus on CT scan. The time to involution varies from 8 weeks (after thyroidectomy) to 4 to 25 months (after antithyroid medication).…”