Polyostotic lymphoma with multiple pathological fractures in a six-month-old cat.

A 6-month-old female neutered domestic shorthair cat was examined for pain and swelling of the distal limbs. Swelling and malalignment of both carpi, dorsiflexion of the distal metatarsals and a mild, multicentric lymphadenopathy were detected on examination. Screening blood tests revealed a biclonal gammopathy, hypercalcemia and atypical leukocytes. Survey radiographs revealed lysis and proliferative changes within the physes. Multiple pathological physeal fractures were present, including the distal radii, metacarpal and metatarsal bones. No treatment was attempted and the patient was euthanased. Histopathology revealed infiltration by monomorphic round cells within the liver, spleen, kidney and bone marrow. Immunohistochemistry revealed strong reactivity to CD20. Clonality assays revealed clonal results for the B-cell loci, consistent with B-cell lymphoma. To the authors' knowledge this is the first report of polyostotic lymphoma with multiple pathological fractures in a cat. The predominantly distal distribution of osseous lesions is rarely reported in dogs and humans.