[Multiple myeloma with significant multifocal osteolysis in a dog without a detectible gammopathy]

Description of a variant of multiple myeloma in a dog lacking the gammopathy normally associated with this type of neoplasm. A Border Collie mongrel was presented with symptoms of progressive hind-leg weakness, lethargy and tiredness, which had started to appear 6 weeks previously. Radiographic examination showed small osteolytic areas in the spinal column, but also diffuse small areas of increased opacity as well as evidence of decreased bone density in the pelvis and of both femoral necks. Moderate regenerative anaemia, hypogammopathy and hypercalcaemia were diagnosed. Computed tomography scans displayed multifocal osteolysis and bone destruction in the skull, spinal column, scapulae, proximal humeri, pelvis and femoral necks. H&E staining of the biopsies showed bone destruction and monomorphic plasmacyotid cell populations, causing infiltrative bone marrow lesions and osteolysis. In many areas neoplastic plasma cell infiltration of the bone marrow was 70% and in some areas reached 100%. The diagnosis was non-secretory multiple myeloma without apparent secretion of paraproteins into the blood.