Localized Thymic Amyloidosis Presenting with Myasthenia Gravis: Case Report

A mediastinal mass was incidentally found on chest radiography in a 46-yr-old woman who had had myasthenia gravis (MG) for 2 months. Computed tomography revealed a 4-cm in size, well-defined, and lobulating mass with nodular calcification that was located in the thymus. Microscopically, the mass consisted of diffuse amorphous eosinophilic materials. These deposits exhibited apple-green birefringence under polarized light microscopy after Congo red staining. Immunohistochemical analysis revealed that they were positive for both kappa and lambda light chains and negative for amyloid A. A diagnosis of localized primary thymic amyloidosis was finally made. After thymectomy, the symptoms of MG were controlled with reduced corticosteroid requirements. Localized thymic amyloidosis associated with MG has not been reported to date.

A Case of Isolated Light Chain Deposition Disease in the Duodenum

Light chain deposition disease (LCDD) is a rare disorder associated with a clonal proliferation of plasma cells, which synthesize abnormal monoclonal immunoglobulin light chains. LCDD is characterized by systemic deposition of light chains in various organs, with the kidneys being most commonly affected. There have been few reports of isolated LCDD. We report a rare case of LCDD limited to a duodenal polyp. A 63-yr-old man visited our hospital for health screening without symptoms in 2009. On gastrofiberscopy, a duodenal polyp was observed. The biopsy showed diffuse infiltration by atypical plasma cells, which were positive for kappa-type light chains by immunohistochemistry. While the patient refused further management, we could find no evidence of recurrence until 2 yr after the initial diagnosis. It has been reported that isolated LCDD has relatively good prognosis compared to systemic LCDD. However, treatment for this disease has not been established yet.