Endocrine Abstracts

Introduction: Grave’s disease (GD) is an autoimmune disease characterized by the development of thyroid-stimulating hormone (TSH) receptor antibodies that have a stimulating effect on the thyroid gland. There is a rare but non-incidental and well-documented association between GD and thymic hyperplasia (TH). Nonetheless, this association is often underdiagnosed in routine clinical practice and the mechanisms behind this association have yet to be thoroughly elucidated. Thymic regression with the resolution of hyperthyroidism is characteristic. We describe one case of TH in a patient with Grave’s disease.

Case Presentation: We present the case of a 40-year-old male with no personal or family history of interest, referred for primary hyperthyroidism. A chest computed tomography (CT) scan had been performed in Primary Care in the setting of constitutional symptoms, and revealed a 3 cm anterosuperior mediastinal mass consistent with TH. No signs or symptoms of myasthenia gravis were noted. A positron emission tomography CT scan was performed in order to exclude a thymoma, revealing no metabolic activity increase. He presented with diffuse goiter, hand tremor and increased heart rate. Laboratory findings showed TSH <0.01 mIU/l [0.380-5.330] with T4L 4.2 ng/dl [0.54-1.24]and positive anti-TSH receptor antibodies (TRAB)(40 U/l, reference range <1.75). Thyroid ultrasound showed an enlarged thyroid with increased vascularity. Based on these findings, the patient was diagnosed with GD and coexisting TH. Since TH is an uncommon but known manifestation of GD, no further investigations of the thymic mass were done and medical treatment of GD was started with a titration regimen of methimazole and propranolol. A conservative and observational approach was taken to monitor TH. Twelve months later and after maintaining a euthyroid state with negative TRAB, a repeat CT scan was performed and revealed total regression of the mass seen on the previous CT.

Conclusion: Mediastinal tumours located in the anterosuperior mediastinal compartment are usually malignant, the detection of an anterior mediastinal mass usually leading to biopsy or even surgical removal. Nonetheless, in Grave’s disease the diagnostic approach is different. Resolution of hyperthyroidism together with back to normal anti-TSH receptor antibodies is associated with regression of thymic hyperplasia. Several hypotheses have been proposed to explain the mechanisms behind the association of GD and TH, including an immunology-based pathogenesis and a direct thymic trophic effect from excess thyroid hormones. Benign evolution as evidenced by regression of thymic hyperplasia after resolution of hyperthyroidism in all cases described in the literature, supports a conservative approach.