Plasmacytoma of the thoracic spine with intracellular amyloid and massive extracellular amyloid deposition.

A 65-year-old woman presented with back pain and a lytic destructive lesion of T-11. Fine-needle aspiration biopsy revealed a granulomatous reaction with unusual signet ring type cells and vacuolated histiocytes. Subsequent resection of the lesion revealed a fibrohistiocytic reaction with extensive amyloid deposition. Immunoperoxidase stains confirmed monotypic kappa light-chain staining. Ultrastructural examination of paraffin-embedded tissue confirmed extracellular amyloid deposition. A unique feature of this case was the finding of intracellular amyloid; the unusual signet ring cells were shown to be plasma cells with intracellular amyloid, and the vacuolated histiocytes also contained amyloid.