Primary Intramuscular T-cell Lymphoma with MUM-1 Expression in a Dog

Background : In both humans and veterinary species, primary intramuscular lymphoma is a rarely reported condition. Limited literature available shows that these tumors are often multifocal, with clinical signs often including limb edema and swelling, and lameness. Signs are typically acute and rapidly progressive. Case Presentation : A 10-year-old castrated male dog with multifocal intramuscular masses was diagnosed as T-cell Lymphoma with aberrant MUM-1 expression. He presented due to rapidly progressive right hindlimb edema. The diagnosis was difficult to achieve in this case due to an unusual pattern of expression of surface markers. A combination of contrast CT, cytology, histopathology, immunohistochemistry, and PARR were necessary to achieve a final diagnosis. The dog had an initial rapid response to doxorubicin, but progressive disease was noted shortly after the third dose was administered. He was then treated with rescue chemotherapy protocols and focal radiation therapy. Despite these aggressive therapies, his disease was further progressive and due to poor quality of life humane euthanasia was pursued 63 days after initial presentation. Conclusions : Intramuscular lymphoma appears to be an aggressive subtype of lymphoma. Diagnosis can be difficult in these cases, and a multi-modal approach is often necessary. While these patients can respond well to chemotherapy and radiation therapy, the response is often short-lived, and prognosis remains guarded for these dogs.