Mrs. K is a 62-year-old woman who notes a 6-month history of worsening midthoracic back pain with marginal relief from increasing doses of ibuprofen. She is a school librarian working in a rural community and married, with 3 children out of the house. An X-ray of the thoracic spine reveals small lytic lesions, which are confirmed on subsequent magnetic resonance imaging (MRI) scans of the thoracic spine and lumbar spine. Blood studies revealed elevated globulin levels prompting the following workup on referral to the medical oncologist: normal serum calcium level, normal serum creatinine levels (0.8 mg/dL), hemoglobin 10.8 g/dL, serum albumin 3.2 g/dL, immunoglobulin G (IgG) κ isotype by serum immunofixation, serum electrophoresis shows an M-protein spike of 3.8 g/dL, total serum IgG 4.7 g/dL, low IgM/IgA, serum free κ light-chain levels 2550 mg/L,...

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