Primary malignant myelomatous pleural effusion

Primary malignant myelomatous pleural effusion (PMMPE) occurs in less than 1% of patients with multiple myeloma and is diagnosed either by visualization of plasma cells on cytology or by positive flow cytometry. The presence of immature plasma cells characterized by high nucleus to cytoplasm ratio, visible nucleolus and presence of Mott cells and Russell bodies are independent poor prognostic factors. The clinician should differentiate PMMPE from secondary pleural effusion as it is associated with a significantly worse prognosis and poor overall survival.