Endocrine Abstracts

JOINT2886

Introduction: Thymic hyperplasia is frequently observed in patients with Graves’ disease. The association between Graves’ disease and thymic hyperplasia was first described in 1912, and up to 38% of patients with Graves’ disease exhibit histological thymic abnormalities. However, the exact mechanism underlying the development of thymic hyperplasia in these patients remains unclear.

Case Report: We present a case report of a 23-year-old female medical student who presented to the outpatient clinic with complaints of palpitations, tachycardia, tremors, anxiety, and a weight loss of 5 kg over three months. She had no eye symptoms. On physical examination, her vital signs were as follows: blood pressure of 110/70 mmHg, heart rate of 130 beats per minute, respiratory rate of 18 breaths per minute, weight of 49 kg, and height of 160 cm (body mass index of 19.14 kg/m²). Laboratory tests revealed a suppressed TSH level of <0.005 μIU/mL (reference range: 0.27–4.2 μIU/mL), elevated free T4 of 4.47 ng/dl (reference range: 0.93–1.7 ng/dl), thyroperoxidase antibody of 397 IU/mL (reference range: 0–34 IU/mL), and thyrotropin-binding inhibitory immunoglobulins of 37 IU/l (reference range: 0–115 IU/l). The anti-TSH receptor antibody was also elevated at 20.5 IU/l (reference range: <1.22 IU/l). A thyroid ultrasound showed a heterogeneous and hypoechoic thyroid gland with increased vascularization. Additionally, a heterogeneous structure was observed below the left thyroid lobe. A CT scan of the neck and chest confirmed the presence of a hyperplastic thymus measuring 27 mm, located below the thyroid gland. Following a neurological evaluation, electromyography (EMG) was performed, and myasthenia gravis was ruled out. The patient was started on Methimazole 5 mg twice daily (2-0-2). After six weeks, she returned for follow-up with no symptoms of hyperthyroidism and a weight gain of 1.5 kg. Laboratory results showed TSH at 0.45 μIU/mL and free T4 at 1.1 ng/dl. A follow-up neck CT scan was scheduled for three months later.

Conclusion: Thymic hyperplasia is a common finding in patients with Graves’ disease. It is important to consider this diagnosis in patients with thyrotoxicosis and a mediastinal mass to prevent unnecessary interventions that could lead to harm. The prognosis is excellent, and treatment with methimazole has been reported to contribute to thymic mass reduction.