Presenting features A 56-year-old black woman with diabetes mellitus was admitted for hypoglycemia and confusion. Her past medical history included breast cancer, for which she had undergone a left lumpectomy and then mastectomy for in-breast recurrence. Her oral intake had decreased during the past month because of increasing discomfort from left-sided chest pain. During this period, she continued to take pioglitazone for diabetes at her originally prescribed dose. The patient's mental status improved quickly after taking orange juice and intravenous glucose, but the chest pain persisted. The pain, which was described as an ache along the left costal margin, increased with palpation, deep inspiration, or coughing. She had recently presented with similar complaints at another hospital where she had been prescribed a muscle relaxant that provided no relief from the pain. She also reported a 14-lb weight loss during the previous 3 months, as well as fatigue, weakness, and aches in her legs and arms. She denied fevers, chills, sweats, abdominal pain, nausea, or recent trauma. Laboratory values at the time of admission were: calcium, 11.8 mg/dL; total protein, 11.1 mg/dL; albumin, 3.2 g/dL; creatinine, 1.0 mg/dL; and hematocrit, 29.3%, with a mean corpuscular volume of 89.3. Chest radiography revealed a lytic lesion in the left lateral fourth rib and left humerus (Figure 1). Serum and urine protein electrophoresis revealed a monoclonal spike in the gamma region consistent with monoclonal gammopathy. The serum spike was quantified at 3.78 g/dL. A skeletal survey showed many small well-defined lytic lesions in the skull (with one 1.5-cm lytic lesion in the upper posterior parietal bone), arms, and legs. A bone scan showed multiple foci of increased uptake in the right and left ribs as well as the proximal portion of the left femur. The peripheral blood smear revealed rouleaux formation (Figure 2) and plasma cells (Figure 3). What is the diagnosis?
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