A 47-year-old man presented with sudden onset of nontraumatic back pain. MRI showed multiple compression fractures within the thoracic and lumbar spine (Fig. 1). Dual-energy X-ray absorptiometry scan demonstrated osteoporosis. Biochemical studies were unremarkable (normal serum and urine protein electrophoresis, parathyroid hormone, testosterone, 25-hydroxyvitamin D, and 24-hour urine calcium). The patient failed conservative management and underwent a laminectomy with spinal fusion. An iliac crest biopsy was performed intraoperatively to look for secondary causes of osteoporosis.Figure 1.MRI showing multiple compression fractures (arrows) along with narrowing of the spinal canal (arrowheads).The biopsy showed replacement of bone marrow with amorphous material which demonstrated apple-green birefringence on polarization (Fig. 2). No monoclonal plasma cells were seen. Liquid chromatography-tandem mass spectrometry detected a peptide profile consistent with AL (light-chain)-type amyloido ...