This patient's presentation is classic for multiple myeloma. Multiple myeloma results in large eosinophilic casts made of Bence-Jones proteins that can be seen on urine microscopy.Multiple myeloma is cancer of monoclonal plasma cells resulting in the production of large amounts of IgG (55%) or IgA (25%). The amount of light chains (Bence-Jones protein) filtered exceeds the resorptive capacity of the tubule. These proteins precipitate and form large eosinophilic casts, which then obstruct the tubule and interfere with renal function. When approaching this question it is important to break down this seemingly vague scenario into symptoms of an elderly man with 1. back pain 2. renal dysfunction 3. Rouleaux formation (non-specific but suggestive of increased protein state) and 4. an abnormal spike on serum electrophoresis. With these symptoms in mind, this becomes a very classic presentation of multiple myeloma. Keep in mind that in an elderly patient with back pain, hypercalcemia and a finding such as a Rouleaux formation or a monoclonal spike that this is highly suggestive of multiple myeloma for Step exams and the most accurate test to confirm this diagnosis is a bone marrow biopsy demonstrating increased plasma cells.Illustration A displays the eosinophilic casts seen with multiple myeloma. Illustration B displays other types of urinary casts. Incorrect Answers:Answer 1: Early satiety and splenomegaly are classic findings in CML. In CML the classic 9:22 translocation and the bcr:abl translocation (Philadelphia chromosome) are pathognomonic. The best initial therapy is imatinib, the definitive therapy is bone marrow transplant.Answer 2: Smudge cells would present in CLL and could be found in an elderly patient with increased white cells. The age of the patient could suggest CLL but the other symptoms are more classic for multiple myeloma. Answer 3: An elevated PSA and a nodular prostate could be found in this patient if they had metastatic prostate cancer to the lower back. This could cause symptoms of lower back pain, hypercalcemia and the chronic picture in this case however the monoclonal spike suggests against this.Answer 5: Normal aging may have a patient with some complains of musculoskeletal pain however the serum findings are certainly abnormal.The incidence of multiple myeloma is increasing in older patients. The classic presentation of multiple myeloma is bone pain, malaise, anemia, renal insufficiency, and hypercalcemia. At early stages of this disease, incidental discovery on routine lab analysis is common (1).