Juvenile polyostotic lymphoma

JSAP 1997

S. J. Langley-Hobbs, S. Carmichael, C. R. Lamb, A. P. Bjornson, M. J. DAY

Background
Lymphoma in dogs is a common malignancy primarily affecting lymph nodes or visceral organs, rarely involving the bones. This case report details a rare presentation of polyostotic lymphoma in an 8-month-old female German Shepherd Dog, emphasizing the significance of recognizing lymphoma in young dogs presenting with polyostotic osteolytic lesions and fractures.

Methods
The study describes a case report with clinical examination, radiographic imaging, histopathology, immunohistochemistry, and postmortem examination. Radiographs revealed bilaterally symmetrical osteolytic lesions in multiple bones. Biopsies and postmortem samples were histologically analyzed to confirm lymphoma, and immunohistochemical staining was performed to assess the tumor's lymphocyte origin.

Results
The dog presented with pathological fractures and multifocal osteolytic lesions in multiple long bones, ribs, and the skull. The lesions were primarily metaphyseal with minimal reactive bone formation. Histologically, neoplastic lymphoblasts infiltrated the spleen, thymus, liver, and bones. Immunohistochemistry failed to positively identify specific T or B cell markers, though cytology was consistent with lymphoid neoplasia. The tumor was classified as high-grade lymphoblastic lymphoma. The condition led to systemic deterioration, and the dog was euthanized.

Limitations
The immunohistochemical analysis did not confirm the lymphoma subtype due to lack of positive staining for T or B cell markers, suggesting possible phenotypic variability or loss of marker expression. Diagnostic alternatives such as protein electrophoresis for monoclonal gammopathy were not performed.

Conclusions
Polyostotic lymphoma, though rare, should be included in differential diagnoses for young dogs with multifocal osteolytic lesions, particularly in metaphyseal regions. The findings highlight the need for thorough diagnostic workups in similar cases to improve understanding and management of this uncommon manifestation.

FIG 1. Radiographs obtained of an eight month old German Shepherd dog with polyostotic lymphoma. Mediolateral view of the right thoracic limb (A), right pelvic limb (B) and detail of a lateral radiograph of the skull (C). There are multifocal, clearly marginated but coalescing osteolytic lesions affecting the metaphyses of the long bones, and the sagittal crest and external occipital protuberance of the skull. These lesions lack sclerotic borders. There are fractures of the distal radius and ulna; periosteal reaction adjacent to the fractures may be callus. A smooth diffuse periosteal reaction affects the right tibial diaphysis (B)

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