Unusual multiple myeloma cutaneous manifestation following nonmyeloablative allogeneic stem cell transplantation.

Skin involvement in multiple myeloma (MM) has been described, but is uncommon.1-4 It usually presents in the form of plasmacytoma or nodular skin lesions that involve a well-demarcated area of the skin. We describe a case of unusual cutaneous involvement in a patient with relapsed MM after nonmyeloablative allogeneic stem cell transplantation (allo-SCT) that presented as a diffuse erythematous rash without any evidence of nodularity. Typically, there is a wide differential diagnosis for such skin rash in these patients including graft versus host disease (GVHD), drug reaction, vasculitis, or cellulitis. Thus, our case emphasizes the need to include myeloma in the differential diagnosis of erythematous skin rash.