Bone lesions of multiple myeloma in three dogs

Three cases of canine multiple myeloma that showed monoclonal IgA gammopathy and bone lesions were examined. One dog was associated with Bence-Jones proteinuria as well. Radiographic examination revealed extensive skeletal involvement of flat bones such as scapula, pelvic bone, costa, and epiphysis of long bones where the hematopoiesis was active throughout the life. Histopathologically, small osteolytic lesions occurred from periosteum and Haversian canal as well as endosteum, and larger lesions were formed by gradual expansion or fusion of small lesions. Osteolytic lesions did not necessarily involve tumor growth, explaining the inconsistent confirmation of tumor cells in biopsy specimens for diagnosis of multiple myeloma and suggesting the possible mechanism for osteolysis by some other humoral factors.