Thymic hyperplasia in Graves’ disease Danilovic DLS et al. CLINICS 2011;66(12):2177-2178 Figure 1 - CT-scan images showing a thymus enlargement before (A) and after (B) treatment for hyperthyroidism due to Graves9 disease, with remarkable shrinkage of the thymus (arrows). There are two morphologic forms of thymus hyperplasia associated with Graves’ disease: lymphoid hyperplasia and true hyperplasia. The first is characterized by a thymus medullary lymphoid-follicle formation that is not visualized as an enlargement of the anterior mediastinal compart- ment.2 In contrast, the second form, true hyperplasia, presents as an increase in thymic tissue. The mechanism of both hyperplasias is not well established and could be caused by excessive stimulation by the thyroid hormone or TRab itself.3,4 Few cases of detectable massive enlargements of the thymus have been reported; most of these cases involved thymectomy or biopsies to exclude the thymomas and treatment of the remaining tissue with hyperthyroidism.5,6 Because the association between Graves disease and thymic hyperplasia is unclear, unnecessary approaches such as sternotomy and transthoracic biopsy may be used.7 In conclusion, thymic enlargement associated with Graves’ disease, especially when a homogeneous mass without a surrounding invasion, calcifications or a cystic image is revealed from a thoracic CT-scan, allows for judicious clinical and radiologic follow-up during the hyperthyroidism treatment. AUTHOR CONTRIBUTIONS Danilovic DLS and Martin RM were responsible for the clinical diagnosis. Caruso P was the first investigator and Marui S was the mentor of the study. REFERENCES 1. Chaer R, Massad MG, Evans A, Snow NJ, Geha AS. Primary neuroendocrine tumors of the thymus. Ann Thorac Surg. 2002;74:1733- 40, doi: 10.1016/S0003-4975(02)03547-6. 2. Gunn A, Michie W. Biopsy of the thymus. British Journal of Surgery. 1965;52:957-63, doi: 10.1002/bjs.1800521212. 3. Murakami M, Hosoi Y, Negishi T, Kamiya Y, Miyashita K, Yamada M, et al. Thymic hyperplasia in patients with Graves’ disease. Identification of thyrotropin receptors in human thymus. J Clin Invest. 1996;98:2228-34. 4. Nakamura T, Murakami M, Horiguchi H, Nagasaka S, Ishibashi S, Mori M, et al. A case of thymic enlargement in hyperthyroidism in a young woman. Thyroid. 2004;14:307-10, doi: 10.1089/105072504323030979. 5. Kirkeby KM, Pont A. Image in endocrinology: thymic hyperplasia in a patient with Graves’ disease. J Clin Endocrinol Metab. 2006;91:1, doi: 10. 1210/jc.2005-1811. 6. Yamanaka K, Nakayama H, Watanabe K, Kameda Y. Anterior mediastinal mass in a patient with Graves’ disease. Ann Thorac Surg. 2006;81:1904-6, doi: 10.1016/j.athoracsur.2005.07.081. 7. Popoveniuc G, Sharma M, Devdhar M, Wexler JA, Carroll NM, Wartofsky L, et al. Graves’ disease and thymic hyperplasia: the relationship of thymic volume to thyroid function. Thyroid. 2010; 20:1015-8, doi: 10.1089/thy.2009.0383. 2178