Endocrine Abstracts

JOINT4

Background: Recognizing thymic hyperplasia secondary to Graves’ disease (GD) is important for avoiding unnecessary investigations and surgeries. However, other causes of thymic hyperplasia or de novo thymic abnormalities after euthyroidism especially the presence of massive thymic hyperplasia should be investigated. The clinical features of myasthenia gravis (MG) and thyroid eye disease (TED) may be similar and thymic hyperplasia may occur in both conditions. This could be a diagnostic dilemma as to whether a conservative approach or investigations should be pursued. Thymectomy in patients with nonthymomatous MG could improve clinical outcomes and reduce the need for immunosuppressive therapy. Herein, we report an interesting case of the coexistence of severe TED and MG with the presence of thymic hyperplasia.

Clinical case: A 40-year-old Thai woman diagnosed with severe TED requiring orbital decompression and intravenous methylprednisolone presented with left eye ptosis and chewing weakness for 1 month. She denied limb muscle weakness, hoarse voice, or difficulty breathing. Her previous history included hypothyroidism after thyroidectomy for GD 18 months earlier. At the initial diagnosis of GD, laboratory tests were notable for highly elevated serum thyrotropin receptor antibody at 25.5 IU/l and then gradually declined to 13.2 IU/l at 6 months after thyroidectomy (reference range is 0 to 1.75 IU/l). Anti-acetylcholine receptor antibody was positive confirming the diagnosis of MG. A chest computed tomography scan showed a 10×9×1.6 cm thymic enlargement. No mediastinal widening on previous chest X-ray (CXR) at the time of thyroidectomy was found. Therefore, thymic hyperplasia-associated MG was suspected and the patient underwent video-assisted thoracoscopic thymectomy. The pathologic results revealed non-neoplastic thymic tissue with focal thymic epithelial hyperplasia. At 1 year later, her symptoms have much improved and she was prescribed only oral azathioprine 50 mg/day without prednisolone. Strabismus and eyelid surgeries had been performed after inactive TED.

Conclusion: Our case highlighted a diagnostic dilemma as to whether a thymectomy is necessary for thymic enlargement in the setting of coexisting GD and MG. Previous CXR and clinical course of hyperthyroidism are important to differentiate between thymic hyperplasia secondary to GD and thymic hyperplasia-associated MG. While thymic hyperplasia secondary to GD is typically benign and improves with the regular treatment of GD, thymic hyperplasia-associated MG might need further investigations and treatments.