Multiple myeloma with infiltration into skeletal muscle after injections of granulocyte‐colony stimulating factors

Multiple myelomas often occur in elderly people with age‐related complications as they age further. A 54‐year‐old man was first admitted with cerebral infarction and multiple myeloma (IgG kappa, stage IIIA) in November 1989. There was partial remission following chemotherapy. The karyotype of the marrow cells was 46, XY, and no p53 gene mutations were detected by polymerase chain reaction and single‐strand conformation polymorphism analysis. In February 1999, chemotherapy (melphalan, vindesine, ranimustine, prednisolone) was administered as a result of aggravation of the myeloma. Later, after daily subcutaneous injection of 50 µg of nartograstim for 6 days to treat febrile neutropenia, the soft tissues around the right eye swelled gradually, but without redness accompanied by an elevation of the serum creatine‐kinase concentration. When nartograstim was discontinued, however, the swelling disappeared and the creatine‐kinase level normalized. Then in July, on the sixth day of daily subcutaneous injections of 75 µg of filgrastim following the same chemotherapy regimen, similar swelling of the soft tissues occurred around the left eye, and was again reversed by withdrawal of the drug. In July 2000, infusion of dexamethasone was conducted, and following daily subcutaneous‐injection of 75 µg of filgrastim for 5 days, the right subclavicular soft tissue became swollen. The patient later died of myocardial infarction and an autopsy revealed an infiltration of myeloma cells into the right subclavicular muscle and bone marrow that was packed with myeloma cells. This case suggests that exposure to granulocyte‐colony stimulating factors enables myeloma cells to proliferate and infiltrate into soft tissues.