Craniomandibular osteopathy
Inherited, self-limiting proliferative bone disease of growing terriers. Bone is laid down on the mandible, tympanic bullae and nearby skull bones, making it painful or impossible to open the mouth.
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What it is
Craniomandibular osteopathy (CMO, "lion jaw") is a non-neoplastic proliferative bone disease of growing dogs. Lamellar bone is resorbed and replaced by coarse woven bone, and new bone forms under the periosteum, so the affected bones thicken irregularly. The process stops around the end of skeletal growth, and the new bone then partly regresses. In the West Highland white terrier it is inherited as an autosomal recessive trait.
Who it affects
Young dogs, usually between 3 and 8 months of age. Typical breeds are the West Highland white terrier, Scottish terrier and Cairn terrier; it has been described occasionally in other breeds, including some large breeds.
Anatomy involved
The changes are usually bilateral and fairly symmetrical. The most affected sites are the body and ramus of the mandible, the tympanic bullae and the region of the temporomandibular joint; the occipital and parietal bones of the skull may also be involved. When the new bone bridges the tympanic bulla and the angular process of the mandible, it may fuse the temporomandibular region and permanently restrict movement of the jaw.
Clinical signs
Pain when opening the mouth or when the head is handled, difficulty picking up and chewing food, drooling, weight loss, and firm, bony swelling along the mandibles. Intermittent fever is common during active phases. With time the temporalis and masseter muscles may atrophy.
Diagnosis
- Breed, age and palpation of firm, symmetrical swellings of the mandibles.
- Radiographs or CT of the skull: irregular, bead-like periosteal new bone on the mandibular bodies and thickening of the tympanic bullae and temporomandibular region.
- Biopsy is rarely needed; it helps to rule out infection or neoplasia in atypical cases.
Treatment
There is no treatment that stops the disease. Management aims at comfort and nutrition until growth ends: NSAIDs or corticosteroids for pain, soft or liquid food and, if the dog cannot eat, a feeding tube. Prognosis is good when the temporomandibular region is spared, because the lesions regress after growth; it is guarded when bony fusion prevents the mouth from opening. Affected dogs, their parents and littermates should not be used for breeding.
References
- Zachary JF. Pathologic Basis of Veterinary Disease, 6th ed. Elsevier (2017)
- Thrall DE. Textbook of Veterinary Diagnostic Radiology, 7th ed. Elsevier (2018)
- Verstraete FJM, Lommer MJ, Arzi B. Oral and Maxillofacial Surgery in Dogs and Cats, 2nd ed. Elsevier (2020)