Localized Thymic Amyloidosis Presenting with Myasthenia Gravis: Case Report
A 46-yr-old woman was referred to Chungbuk national university hospital for thymectomy in February, 2013. Two months ago, she admitted for first developed ptosis, weakness in the neck, and dyspnea, and was diagnosed with acetylcholine receptor-positive MG. A chest computed tomography (CT) scan revealed a mass with calcification in the anterior mediastinum, which was suggestive of thymoma (). While undergoing cholinesterase inhibitor (Mestinon®) therapy, the patient developed a myasthenic crisis and was given immunoglobulin (Ig) therapy for 5 days under managed ventilator care. Treatment with corticosteroids then continued for a month. After the symptoms regressed, the patient was discharged. She visited the hospital again 2 months later for resection of the mediastinal mass. Given the clinical impression of thymoma-associated MG, mass resection and total thymectomy were performed.\nMacroscopically, the resected mass, which measured 4×3×1.5 cm, was a relatively well-demarcated nodule that was surrounded by fat. The cut section was hard, yellow to gray, and calcified (). Microscopically, the mass was composed of amorphous eosinophilic hyaline materials surrounding islands of thymic tissues (). Stromal calcification and ossification were noted. The associated inflammatory reaction consisted of small lymphocytes and occasional plasma cells. These eosinophilic substances displayed apple-green birefringence under polarized light microscopy after Congo red staining (). Immunohistochemical analysis revealed that they were positive for kappa and lambda light chains and negative for serum amyloid A. These findings were consistent with primary (light chain) amyloidosis. Further examinations were done to rule out plasma cell dyscrasia or lymphoproliferatvie disorder. The serum IgG, IgA, and IgM levels were normal. Serum and urine protein electrophoresis did not detect any abnormal bands. Serum and urine immunoelectrophoresis did not indicate any definite abnormalities. The serum calcium levels were also within normal limits. To screen for systemic amyloidosis, complete blood count, erythrocyte sedimentation rate, echocardiogram, basic metabolic and biochemical panel, and liver function tests were performed. All returned values that were within normal limits. This suggested that the thymic amyloidosis was localized. Therefore, the final diagnosis of primary localized amyloidosis that only involved the thymus was made. The symptoms of MG were relieved dramatically after thymectomy.