Intramedullary deposits of hydroxyapatite crystals in a patient with rheumatoid arthritis

A 63-year-old women with a 12-year history of rheumatoid arthritis (RA) had calcific deposits in the periarticular soft tissues with subsequent involvement of the medullary canals of adjacent bones. Except for the RA, there was no evidence of other abnormalities of the bones or mineral homeostasis. Chemical analyses of the deposits identified the crystalline material as apatite. Although the deposition of apatite in the soft tissues of RA is known to occur rarely, this is the first known case of intraosseous apatite deposition.