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.