Successful Treatment of Renal Cell Carcinoma Associated with Hypertrophic Osteopathy in a Cat.

An eight-year-old spayed female Abyssinian cat presented with lameness. Palpation revealed swelling, heat, and a reduced range of motion in the stifle and tarsal joints in both hind limbs. A radiographic examination of both hind limbs revealed periosteal proliferation from the distal tibia to the tarsal and metatarsal bones, which suggested hypertrophic osteopathy. Thorax and abdominal radiographic examinations were performed to identify the primary disease. Complete blood count and routine serum biochemistry tests revealed no abnormalities. No obvious anomalies were evident in the thoracic radiograph; however, a mass was observed near the left kidney on an abdominal radiograph. An abdominal ultrasound was performed, which revealed a hypoechoic renal mass located in the caudal pole of the left kidney. The left nephrectomy was performed after exploration of the abdominal cavity confirmed an abnormality in the left kidney. A histopathological examination revealed renal cell carcinoma. The cat was subsequently fed on a renal prescription diet but received no additional treatment. The periosteal lesion in the distal tibia regressed over time, but the lesions remained in the talus and metatarsal bones. At 1670 days following surgery, blood tests indicated that urea nitrogen and creatinine were above the normal range. In addition, urinalysis revealed an isosthenuria. However, the cat survived over 4500 days following surgery.