Solitary osseous plasmacytoma of the orbit with amyloidosis.

A 40-year-old woman with an orbital lesion presented with a history of slowly progressive proptosis. A thorough systemic workup did not reveal any stigmata of multiple myeloma, and she was treated with a course of orbital radiotherapy. Histopathologic studies of the biopsy specimen revealed a proliferation of neoplastic plasma cells, which produced monoclonal lambda light chains surrounding concretions of congophilic, amorphous material. The lesion was diagnosed as a solitary osseous plasmacytoma of the orbit containing amyloid.