Disseminated B-cell lymphoma of the urogenital tract in a guinea pig (Cavia porcellus)

A 4-year-old, 0.81 kg, female intact, American guinea pig (Cavia porcellus) was presented for a one-day history of perianal swelling. Physical examination revealed a body condition score of 2 out of 9, a distended abdomen that was painful on palpation, an abnormal vulvar conformation that was enlarged, edematous, ulcerated, and erythematous with adhered foreign material, and a 1 × 1 cm firm mass of the right mammary gland. Hematology revealed a marked lymphocytosis and heterophilia, and a biochemistry panel revealed elevated albumin, alkaline phosphatase, and sodium. Radiographs and abdominal ultrasound showed a caudal abdominal mass effect, edematous enlargement throughout the urogenital tract, a mass effect in the right mammary gland, gas distention of the cecum and stomach, and a markedly thickened urinary bladder wall with probable uroliths and mineralized sediment. Due to the extent of disease, euthanasia was elected and a necropsy with histopathology was performed. On gross examination the vulva and surrounding tissues were firm and swollen, bilateral masses were identified expanding each mammary fat pad, and the inguinal and mandibular lymph nodes were bilaterally enlarged. Histopathologic examination revealed a monomorphic population of neoplastic lymphocytes effacing the uterus, broad ligament, vulva, kidneys, urinary bladder, lung, liver, heart, leptomeninges, thyroid, and bone marrow. The diagnosis was determined to be disseminated B-cell lymphoma via PAX5 immunohistochemistry. This is the first case of disseminated B-cell lymphoma in a guinea pig that predominantly affected the urogenital tract. Lymphoma should be considered as a differential diagnosis in guinea pigs with perineal enlargement.