Craniomandibular Osteopathy (CMO)

Craniomandibular osteopathy (CMO) is a non-cancerous disorder that almost exclusively affects the bones of the head in dogs. It is also called mandibular periostitis, temporomandibular osteodystrophy or "lion jaw."

The cause of CMO is believed to be hereditary. Terriers are prone to the disorder. West Highland white terriers are the most commonly reported breed to be affected with CMO, with Scottish terriers, cairn terriers, Boston terriers and bullterriers also having a higher than normal incidence. It has been reported in non-terrier breeds, but this is uncommon.

The age of onset of clinical signs is usually three to eight months. There is no sex predilection, with males and females affected equally. Neutering and spaying seems associated with reduced risk of the disorder.

The disorder is usually self-limiting, but may require medication to make the dog comfortable. 

What to Watch For

Swollen painful mandible (jaw)

Excessive drooling

Difficulty picking up food

Pain upon opening of the mouth

Diagnosis

Radiographs 

Serum chemistry profile

Biopsy

Treatment

No treatment

Glucocorticoids

Non-steroidal anti-inflammatory drugs (NSAIDs)

Home Care and Prevention

Administer pain medications as prescribed and feed special diets as prescribed.

There are no specific preventive care measures. People seeking purebred terriers, especially West Highland white terriers, should question breeders carefully about the occurrence of the disorder in any lines, as CMO is inherited in Westies, and is believed to be inherited in Scottish terriers as well.