Primary multifocal muscular T-cell lymphoma with cutaneous involvement in a dog: A case report and review of the literature.

Canine lymphoma represents a heterogeneous group of lymphoid neoplasms, with multicentric nodal lymphoma being the most common presentation. Musculoskeletal involvement is uncommon, and primary muscular lymphoma is a very rare presentation. Only a few cases have been described in dogs, which were of variable classification and immunophenotype. Here, we report the case of a 5-year-old female neutered Beagle that presented with an intramuscular mass on the right shoulder and associated lameness and lethargy. One month after initial presentation, multiple cutaneous nodules appeared on the head, and staging with advanced imaging revealed additional masses affecting other muscles. Cytology, histopathology, immunohistochemistry, and PCR for antigen receptor rearrangements of one of the muscle masses and skin lesions supported a diagnosis of peripheral T-cell lymphoma with large granular lymphocytes at both sites. The dog was euthanized after diagnosis due to the poor prognosis. This is the first report of primary muscular peripheral T-cell lymphoma with large granular lymphocytes and cutaneous involvement in the dog. Despite being a rare presentation, lymphoma must be considered a differential in dogs presenting with a discrete, intramuscular, soft tissue mass.