Hypertrophic osteopathy secondary to pulmonary sarcoma in a cat

A case of hypertrophic osteopathy secondary to a pulmonary spindle cell sarcoma is described. The 9-year-old male cat presented with a 1-month history of decreased appetite, decreased activity and progressive lameness with swelling and pain of all four limbs. Thoracic radiographs showed a soft tissue opaque mass in the left caudal lung lobe. Radiographs of all limbs showed extensive periosteal new bone formation of uniform opacity demonstrating a 'palisading' pattern. The lung mass was removed at exploratory thoracotomy; histopathological examination diagnosed a low-grade spindle cell sarcoma. Prior to surgery, the cat had a non-specific conjunctivitis that resolved spontaneously following lobectomy raising the possibility of a paraneoplastic association. The lameness also resolved; six months after surgery, the periosteal palisading of new bone on the long bones had remodelled, and there was no evidence of pulmonary metastases.