Initial disease presentation with myelomatous pleural effusion is an ominous sign for multiple myeloma: report of a case emphasizing cytological features and ancillary studies.

Multiple myeloma (MM) is a marrow-based, multi-focal neoplastic proliferation of clonal plasma cells. Myelomatous pleural effusion (MPE) is considered a distinctive form of extramedullary disease and usually develop in disease progression or recurrence, but rarely at initial disease presentation of MM. Herein we report a 47-year-old male patient with MM who presented initially with MPE. The typical cytological features (eccentric nuclei and amphophilic cytoplasm with paranuclear hof), flow cytometric immunophenotyping, and cell block preparation with immunohistochemistry confirmed MPE. After establishing the diagnosis of stage III myeloma through bone marrow study, laboratory and radiological corrections, the patient was treated with chemotherapy and palliative radiotherapy. Unfortunately his disease progressed and he passed away in six months. Our case illustrated the importance of detailed cytological examination with ancillary studies for the challenging diagnosis of an extremely rare initial disease presentation of MM with MPE, which is an ominous sign.