Multiple myeloma recurring as small intestinal polyposis after autologous hematopoietic stem cell transplantation.

A 52-year-old woman was diagnosed with BJP-λ multiple myeloma (MM) in November 2012. She was treated with six cycles of bortezomib and dexamethasone, resulting in a very good partial response. The patient underwent autologous peripheral blood stem cell transplantation (PBSCT) 6 months after the diagnosis, and clearly achieved a complete response thereafter. She again suffered chronic abdominal pain with spontaneous remission 9 months after the PBSCT, and, 2 months thereafter, was hospitalized due to intestinal obstruction. Two small intestinal intussusceptions and polyposis in the small intestine were found on abdominal computed tomography. As conservative treatment produced no improvement, partial resection of the small intestine was performed. The pathologic review clearly demonstrated the polyps to have atypical plasma cell infiltrates in the mucosa of the small intestine involving all layers. Immunohisto-chemistry and FISH analyses yielded positive results for CD138, CD79a, and λ light chain, consistent with extramedullary relapse of MM. It is very rare for MM to present with polyposis in the small intestine. There have been no reports describing such a case after autologous PBSCT.