Localized myofibroblastic proliferation in the neck of a patient with an IgG myeloma

We describe a myofibroblastic proliferation in the neck and lower part of the face involving skin and muscle of a 68-year-old female patient with an IgG kappa myeloma. Biopsies showed a fusocellular proliferation with scarce pseudoganglion cells involving the superficial fascia and the cutaneous muscle of the neck. The proliferative cells showed immunohistochemical and ultrastructural features characteristic of myofibrobasts with a proliferating cell nuclear antigen index of 48%; 42% of the cells displayed HLADR-positive membrane staining. Cellular proliferation subsided following the use of immunosuppressive drugs. Eight months after initial consultation, the patient developed polymyositis without a proliferative component and died of aplastic anemia.