Exostosis

Multiple exostosis, also called osteochondromatosis, is a hereditary disorder transmitted by an autosomal dominant gene and characterized by multiple growths near the ends of long bones, ribs, and vertebrae. These growths practically can be seen on any bone except the skull. The genetic abnormality results in a defect at the ends of the bone at an early age. Benign, bony outgrowths develop often capped by cartilage. A small number undergo tumor-like transformation.

Affected animals show forelimb lameness and are in great pain. The disease occurs predominantly in young dogs. The masses continue to grow until the skeletal maturation is complete. Treatment with non-steroidal anti-inflammatory drugs is not effective and usually unnecessary unless it causes serious neurological complications. If the mass compresses the spinal cord, a surgical procedure will be performed to remove the growth.

The prognosis depends on the number, location and surgical accessibility of the masses and is usually good if it does not transform into a cancerous tumor. Continuous or renewed growth past the time of skeletal maturity is considered to be a malignant condition.

The condition also occurs in cats, but they usually live less than a year after onset of signs due to the progressive nature of the disease in cats.