This case report describes a 60-year-old female patient who presented with shortness of breath, cough, fever, weight loss, and bone pain. Clinical examination found edema, diminished breath sounds, dullness on chest percussion, and bony tenderness. Imaging showed pleural and pericardial effusions, thickening, and osteolytic bone lesions. Laboratory tests found anemia, elevated inflammatory markers, and monoclonal gammopathy. Differential diagnoses considered included multiple myeloma, tuberculosis, and malignancy. Further testing of plasma proteins found monoclonal gammopathy, supporting a diagnosis of multiple myeloma with polyserositis.