Fibrodysplasia ossificans in a German shepherd dog

Bilateral cervical heterotopic ossification, associated with a thoracic limb lameness, occurred in an adult German shepherd dog. One of the lesions, thought to be the cause of the lameness, was surgically removed and the lameness resolved. The lesion was classified morphologically as fibrodysplasia ossificans. A similar, smaller lesion was present over the cranial distal scapular border. The causes of ectopic ossification, as described in the veterinary literature, are reviewed and compared with myositis ossificans in humans. Non-progressive fibrodysplasia ossificans has been described in cats, but this appears to be the first report in the dog. It is postulated that the heterotopic ossification resulted from the metaplastic change of calcinosis circumscripta lesions.