If your dog is having trouble eating, this can be a sign of jawbone enlargement making it hard for him to open his mouth. Jawbone enlargement, or CMO, causes the upper and lower jawbones to become enlarged by extra bone growth. This affects the joint in your dog’s jaw that helps him open his mouth, making it harder to eat. CMO can also invade your dog’s nasal cavity, making it difficult to breathe. The bones involved in this condition are the mandible (lower jaw), tympanic bullae (bone which surrounds the middle ear), and temporal region (skull bone) which forms with the temporo mandibular joint in the lower jaw.

Jawbone Enlargement, or CMO (craniomandibular osteopathy), is a painful disorder of the bones in a dog’s skull. Excessive bone growth of the jaw, around the ears, and above the eyes is most often seen when the dog is young; between four and eight months old.

Your dog may try to mask his pain because dogs seem to be of the stoic type. In order to avoid serious secondary complications, do not hesitate to take your dog to the veterinarian immediately if you see any of the symptoms below.

Jawbone enlargement is thought to be caused by a dog’s recessive genes since it has been found most often in terrier breeds. However, CMO has been found in other breeds, such as the Boxer, Bulldog, Great Dane, Bullmastiff, Akita, Shetland Sheepdog, and Doberman Pinscher. The cause in these cases may be due to a growth hormone disorder.

A physical examination will be done by your veterinarian, with special care to palpate the jaw area, and determine pain level while working the jawbone. The veterinary technician will do a CBC, blood chemistry panel, and urinalysis to rule out any other illnesses.

 Multiple digital radiographs (x-rays) of the skull will be needed. The veterinarian will be measuring the thickening of the skull, jawbone, and soft palate. He may also be looking for narrowing of the sinuses, which can be causing your dog to have trouble breathing.

Ultrasound, MRI, and CT scans may also be necessary. The veterinarian may also take biopsies of the bones in the area to rule out other illnesses.

Prednisone or a nonsteroidal anti-inflammatory drug (NSAID) will be prescribed for swelling. Your veterinarian may also prescribe pain medicine to help manage pain. The disorder has been known to disappear on its own when the dog is finished growing. Nutrition is vital during this difficult time; your veterinarian may prescribe a special high calorie liquid diet in order to keep the health of your pet at the forefront. 

If the jawbone enlargement (CMO) does not stop on its own, the veterinarian will work with you to devise a treatment plan. While the pain and swelling are manageable with medication, if it continues to get worse it will eventually cause the inability to eat or breathe, and can compress the brain enough to cause coma and death. Many owners decide to euthanize their dog if it gets too painful or their quality of life is suffering.