Juvenile cranial hyperostosis
Juvenile cranial hyperostosis (Craniomandibular osteopathy, calvarial hyperostosis, lion's jaw) is a rare idiopathic proliferative bone disease of dogs characterized by bony malformations in the mandible and calvarium.
In the West Highland White Terrier, an autosomal recessive genetic disease is suspected, and is associated with generalized bony changes such as bilateral angular carpal deformity with limb bone biopsies confirming similar bony changes to those found in the mandible and calvarium.
A breed predisposition is observed in the Pit Bull Terrier, Scottish Terrier, West Highland White Terrier, Bull Mastiff, Akita, Boston Terrier, Cairn Terrier, Labrador Retriever, Great Dane, Doberman Pinscher, Boxer, Shetland Sheepdog, Pyrenean Mountain Dog and English bulldog.
Clinical signs in affected dogs include painful mastication, pain upon opening the mouth, intermittent pyrexia, ptyalism and bilateral firm swellings of the mandible. Lameness (due to joint deformities) and proprioceptive deficits (due to brainstem compression) are not uncommon.
Blood tests are usually unrewarding, although mild hyperphosphatemia and changes in serum alkaline phosphatase may be found.
Diagnosis ususally requires radiographic, CT or MRI imaging, which illustrates symmetrically enlarged mandibular bodies due to dense osseous proliferation. On ultrasonography, enlarged tympanic bulla, fusion of the temporomandibular joint or auditory canal involvement may also be evident. In large breed dogs, the lesions are usually confined to the mandible, while the parietal crest, frontal, lacrimal, and maxillary bones may be affected in small breed dogs.
Histopathology is usually required for a definitive diagnosis and usually reveals osteolysis of the periosteal or subperiosteal region and thickening of bony trabecula.
Treatment is usually conservative in most cases, with anti-inflammatory medication. Use of prednisolone is controversial and surgical attempts to remove excess bone have been unsuccessful, although a hemimandibulectomy may be performed as a salvage procedure for cases where the jaws can not be opened.
The prognosis is guarded when extensive bone changes involve the temporomandibular joint. Some regression of the bony changes may occur following growth plate closure.
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