Endocrine Abstracts

Introduction: Thymic hyperplasia is a rare manifestation of Graves disease. In this report, we describe a female with Graves’ disease and a neck mass that was associated with thymic hyperplasia.

Case report: A 28-year-old woman was referred to our division for the evaluation of palpitations. Thyroid function tests were associated with thyrotoxicosis. Thyroid receptor antibody (TRAb) was found to be 22.3 U/l (positive: >14 U/l). Sonography showed bilateral enlargement of thyroid lobes, typical ‘thyroid inferno’ pattern and also a homogenous mass of 10×15×25 mm in dimensions, at the inferior of the thyroid. Magnetic resonance imaging demonstrated that the mass was a homogenous anterior mediastial lesion plunging to the neck, compatible with hyperplasia of the thymus. Thymic hyperplasia related to GD was suggested and follow up was recommended. She was treated with metimazole. At the 3rd month of therapy euthyroidism was obtained but there was no significant change in either the size or the sonographic characteristics of the mass. At the 6th month of therapy neck ultrasonography did not reveal any regression of the mass. Total thyroidectomy and mass extirpation were performed and pathological examination was consistent with chronic lymphocytic thyroiditis and thymic hyperplasia.

Conclusion: Elevations in circulating thyroid hormones are suggested to cause thymus hyperplasia in Graves disease. It must be noted that microscopic changes in the thymus can be detected in one third of patients but massive enlargement is rare. This presented patient has two different features when compared with the previously reported cases. First, she presented with a neck mass instead of a mediastinal mass. This is probably due to a different growth pattern of thymus from mediastinum towards the cervical area Second, the hyperplastic thymus did not regress after anti-thyroid treatment. We suggest that additional factors rather than the level of circulating thyroid hormones may be involved in the pathogenesis of thymic hyperplasia in Graves’ disease.