A 70-year-old man complains of 2 months of low back pain and fatigue. He has developed fever with purulent sputum production. On physical examination, he has pain over several vertebrae and rales at the left base. Laboratory results are as follows:
The definitive diagnosis is best made by which of the following?
A. 24-hour urine proteinMultiple myeloma would best explain this patient’s presentation. The onset of myeloma is often insidious. Pain caused by bone involvement, anemia, renal insufficiency, and bacterial pneumonia often follow. This patient presented with fatigue and bone pain, then developed bacterial pneumonia probably secondary to Streptococcus pneumoniae, an encapsulated organism for which antibody to the polysaccharide capsule is not adequately produced by the myeloma patient. There is also evidence for renal insufficiency. Hypercalcemia is frequently seen in patients with multiple myeloma and may be life threatening. Definitive diagnosis of multiple myeloma is made by demonstrating greater than 30% plasma cells in the bone marrow. None of the other findings are specific enough for definitive diagnosis. Seventy-five percent of patients with myeloma will have a monoclonal M spike on serum protein electrophoresis (as shown in the illustration), but 25% will produce primarily Bence-Jones proteins, which, because of their small size, do not accumulate in the serum but are excreted in the urine. Urine protein electrophoresis will identify these patients. Approximately 1% of patients with myeloma will present with a nonsecretory myeloma; the diagnosis can be made only with bone marrow biopsy. The bone scan in myeloma is usually negative. The radionuclide is taken up by osteoblasts, and myeloma is usually a purely osteolytic process. Renal biopsy might show monoclonal protein deposition in the kidney or intratubular casts but would not be the first diagnostic procedure. Rouleaux formation, although characteristic of myeloma, is neither sensitive nor specific.