Castleman's disease is an atypical lymphoproliferative disorder of unknown etiology, which might be associated with various clinical conditions, including autoimmune diseases and malignant neoplasms. We report the case of a 72-year-old female patient who was referred to the thoracic surgery department of Getúlio Vargas University Hospital, in the city of Manaus, Brazil, for the resection of a posterior mediastinal tumor. Three months prior, the patient had been admitted to the ICU with signs of severe dyspnea, at which time she was diagnosed with myasthenia gravis. After the resection of the mediastinal tumor, the histopathological examination revealed hyaline vascular-type Castleman's disease, complicated by follicular dendritic cell sarcoma. At this writing, the patient was being treated with an anticholinesterase agent and corticosteroids for the control of myasthenia gravis.

Keywords: Giant lymph node hyperplasia; Dendritic cell sarcoma, follicular; Myasthenia gravis; Mediastinal diseases.