Craniomandibular osteopathy (CMO) is a bizarre disease affecting the bone growth of the jaw and face in puppies of certain breeds. These breeds include:
- West Highland white terrier
- Scottish terrier
- Cairn terrier
- Boston Terrier
- Labrador Retriever
- Doberman pinscher
- English Bulldog
- Great Dane
The majority of cases occur in the West Highland white terrier, which accounts for the more familiar name for CMO, “Westie jaw.”
In Westie jaw, new bone is developed for no apparent reason. The most common locations are in the bones of the face, including the eye socket and along the lower jaw.
This can be quite a problem if new bone is deposited into the hinge joint of the jaw — it restricts the puppy’s ability to open his mouth. In particularly serious circumstances it may be so severe the puppy cannot open the mouth, in which case a feeding tube is necessary or, unhappily, euthanasia must be considered as a kinder alternative.
Westie jaw is most likely to start causing problems between 4 and 8 months of age, with discomfort and pain around the face and jaw.
Someone with one of these dogs must first become aware of the puppy being a messy eater, spreading food on the floor and dropping treats out of his mouth. This is because of the puppy cannot physically open his mouth wide enough to eat properly and has difficulty lapping and chewing food. As the condition worsens, the puppy may lose weight and have a scruffy, unkempt coat as he cannot groom himself.
This is one of those conditions that may be mild, severe or any shade in between. Some puppies are only mildly affected, whereas others may be so bad that they can’t open their mouth sufficiently to lap water. The bone deposits are permanent, and in the face of such disability it may be necessary to consider euthanasia to stop any suffering.
CMO is neither a cancer nor is it caused by infection — it happens as a result of bone proliferation in growing dogs.
The most likely explanation is that this is a genetic condition with inappropriate gene coding for extra bone growth. This theory seems especially likely given the strong link between CMO and Westies (among other breeds).
Diagnosis is usually made on the basis of a physical exam of the patient and radiographs.
These puppies are often uncomfortable when the face or jaw is touched. Sometimes they have difficulty opening their mouths, even when anesthetized. Some cases are discovered at neutering because the veterinarian cannot physically open the mouth wide enough to pass a breathing tube for the anesthetic gas into the dog’s windpipe.
Radiographs will show extra bone along the jawbone or around the jaw’s hinge joint.
Unfortunately, there is no treatment that will halt the bone deposition.
Therapy is largely symptomatic pain relief to try and keep the puppy as comfortable as possible. Once the puppy has finished growing, the CMO stops developing. Attempts to surgically remove the additional bone are disappointing because it just regrows.
Dogs with CMO should never be bred from because they will pass the condition onto their puppies. Indeed, the dam and sire that produced the pup with CMO should not be mated together again because they will produce more affected puppies.
In this video, Dr. Karen Becker, DVM, discusses more:
- “Craniomandibular osteopathy in dogs.” Watson, Adams & Thomas. Compend Contin Educ Pract Vet 1995, 17: 911–921.
- “Craniomandibular osteopathy.” Tilley & Smith. The Five-Minute Veterinary Consult. Publisher: Williams & Wilkins. 486–487.
This pet health content was written by a veterinarian, Dr. Pippa Elliott, BVMS, MRCVS. It was last reviewed Jan. 3, 2016.