Craniomandibular Osteopathy (CMO) in Dogs

Craniomandibular Osteopathy (CMO) in Dogs

Overview of Craniomandibular Osteopathy (CMO) in Dogs

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

Signs of craniomandibular osteopathy in Dogs may include: 

  • Swollen painful mandible (jaw)
  • Excessive drooling
  • Difficulty picking up food
  • Pain upon opening of the mouth
  • Diagnosis of Craniomandibular Osteopathy (CMO) in Dogs

  • Radiographs
  • Serum chemistry profile
  • Biopsy
  • Treatment of Craniomandibular Osteopathy (CMO) in Dogs

  • 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.

    In-depth Information on Canine Craniomandibular Osteopathy 

    Craniomandibular osteopathy (CMO) is a skeletal disease that occurs mainly in certain breeds of young terriers, although occasionally, non-terrier breeds are affected. The disease was first reported in England in 1958. When it affects large breeds, there is a greater tendency to show involvement of only the mandibles, and the condition seems to be less painful in large breeds.

    There is no gender predilection, and males and females are affected equally. There is a tendency, however, for a reduction of the incidence of disease in dogs that are neutered or spayed.

    Clinical signs usually develop when the dog is between 3 and 8 months of age, although there have been cases as young as two weeks and as old as 11 months. The cause of the disorder remains unknown, although there is evidence that the disease is inherited in West Highland white terriers, and possibly other terrier breeds.

    Dogs with the disorder usually show signs of a swollen painful jaw, drooling, difficulty picking up food and pain on opening the mouth. Some dogs have an intermittent fever.

    Severely affected dogs show atrophy of the muscles of mastication (chewing). X-rays are the main method of confirming the diagnosis. Both sides of the jaw are usually affected, although some dogs are affected only on one side. A biopsy may be necessary to confirm the diagnosis in breeds for which this disorder is uncommon, especially if only one side of the jaw is affected. The disorder usually resolves on its own, although anti-inflammatory drugs may help reduce some of the clinical signs. Occasionally, a dog is euthanized because of inability to relieve the extreme discomfort.


    In-depth Information on Diagnosis

  • Radiographs. X-rays are needed to confirm the diagnosis of CMO. Most dogs show involvement on both sides of the face. Most of the time, the jaws are affected symmetrically, but occasionally, the dog is affected on one side only. On X-rays, proliferation of bone on both mandibles (84 percent of cases) is evident. In addition to the mandible, the tympanic bullae, which is the bony structure that houses the middle and inner ear, and the petrous temporal bone of the skull are commonly affected (51 percent of cases). Rarely, the mandible is not affected at all, but other parts of the skull show thickening or proliferative changes.
  • Serum chemistry profile. Complete blood counts and urinalysis are normal. Serum chemistry profiles do not show any specific changes. A few dogs have been reported to have high cholesterol, high phosphorus, high alkaline phosphatase and/or high creatine kinase, in any combination. These findings are non-specific. The increases in alkaline phosphatase and phosphorus are common findings in growing dogs, and are unlikely to be related to the presence of CMO.
  • Biopsy. Diagnosis of CMO is relatively easy in cases with typical clinical signs and X-ray appearance. Biopsy may be necessary only in atypical cases, as in rarely affected breeds in which the disease is confined to the mandible only, especially if the disorder is unilateral.
  • In-depth Information on Therapy 

    No satisfactory treatment trials have been done for CMO in dogs. The disease is usually self-limiting, with the progression of the disease slowing down at around 11 to 13 months of age. Sometimes, it is followed by a slow regression of the disorder, although radiographic abnormalities or impaired function may remain. Several drugs have been tried, however, with good response.

  • Glucocorticoids. These drugs, at anti-inflammatory dosages, may reduce pain and discomfort, although they don’t have any effect on the bony changes involving the mandible.
  • Non-steroidal anti-inflammatory drugs (NSAIDs). NSAIDs such as aspirin or phenylbutazone have also been reported to relieve some of the pain and discomfort associated with the disorder.
  • Follow-up Care for Dogs with Craniomandibular Osteopathy

    Optimal treatment for your dog requires a combination of home and professional veterinary care. Follow-up can be critical, especially if your pet does not rapidly improve. Administer all prescribed medication as directed. Alert your veterinarian if you are experiencing problems treating your dog.

    Return to your veterinarian for follow-up radiographs, to monitor progression and/or resolution of the disorder.

    The prognosis for affected dogs is guarded when extensive bone changes are present and are affecting the tympanic bullae and petrous temporal bone area. These animals may develop fusion of bones in this area, permanently restricting or preventing jaw movements and hindering the act of eating. The prognosis is better in dogs that are mildly affected. The disease often stops progressing around 11 to 13 months of age, and then may regress partially or completely.

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