THYMIC HYPERPLASIA IN GRAVES’ DISEASE

A DIAGNOSTIC AND MANAGEMENT CHALLENGE

Abstract

INTRODUCTION/BACKGROUND
Thymic hyperplasia is a recognized but frequently underappreciated entity associated with Graves’ disease (GD). It is often misinterpreted as a mediastinal mass, potentially leading to unwarranted biopsies or surgical intervention. The underlying pathophysiological mechanisms remain poorly understood. Spontaneous regression of the mediastinal mass following euthyroidism with effective thyrotoxicosis treatment supports a benign etiology. Here, we present a case of a young female with GD and an incidentally discovered anterior mediastinal mass, highlighting the diagnostic complexities that necessitated a multidisciplinary approach.

CASE
A 21-year-old female presenting with a large goiter, a thyrotoxic state (FT4 >100 pmol/L, TSH 0.01 mU/ml and anti-TSH receptor Ab >40 IU/L) with no thyroid ophthalmopathy was diagnosed with GD. Despite medical management, adequate control of her thyroid hormone levels proved to be challenging, prompting a surgical consultation for a potential thyroidectomy. To assess the extent of the goiter, computed tomography (CT) imaging was performed, revealing a grossly enlarged thyroid gland with mild tracheal narrowing and a well-defined, solid, enhancing 5.6 cm × 6.4 cm × 4.3 cm anterior mediastinal mass.

Given the initial concern for an ectopic thyroid gland or malignancy, performing an invasive biopsy was considered. However, a multidisciplinary team consisting of experts from endocrinology, surgery, respiratory medicine, radiology, and nuclear medicine reviewed the findings and concluded that the mass was most consistent with thymic hyperplasia. Considering the high surgical risk, a conservative approach was pursued, with the patient undergoing radioiodine therapy for thyrotoxicosis and serial imaging to monitor the mediastinal mass. Long-term outcomes are yet to be seen.

CONCLUSION
This case underscores the diagnostic challenges posed by thymic hyperplasia in patients with GD and the potential for misdiagnosis as a mediastinal pathology. Awareness of this association is crucial in order to avoid unnecessary surgical interventions. A multidisciplinary approach is essential for accurate diagnosis and optimal management, promoting a conservative therapeutic strategy when appropriate.