Craniomandibular Osteopathy

Craniomandibular osteopathy (CMO) is an uncommon inflammatory disease of juvenile dogs characterized by bone proliferation and remodeling of the mandibles [1-31]. The temporomandibular joint is often affected, and involvement (thickening) of other bones of the cranium is common. Pain associated with CMO is typically moderate to severe. Difficulty eating, deformity, and/or pain when opening the mouth are common presenting complaints. West Highland terriers and Scottish terriers are the predominant breeds affected. Long bones may also infrequently be affected, with or without clinical signs of lameness and/or pain with palpation. CMO typically regresses as normal bone formation ends at about 1 year of age [1].

CMO was first reported in 1958 in five West Highland terriers, and in 1959 in West Highland white and Scottish terriers [1,2]. Clinical and radiographic diagnosis was initially neoplasia. However, histopathology indicated non-neoplastic mandibular periostitis with osseous and chondromyxomatous proliferation [1]. Synonyms for CMO include mandibular periostitis, calvarial hyperostosis, idiopathic hyperostosis of the calvaria, and lion jaw [1,3,4].

A Veterinary Medical Data Base (VMDB) survey was perform for this chapter from 1994-2004 and reported a total of 29 CMO cases. Review of the literature reported 65 CMO cases [4-24], some of which predated the years of the VMDB survey whereas others may have also been included in the VMDB study. In addition, cases have been reported in the literature that may be atypical CMO cases. Pastor et al. reported a disease he termed calvarial hyperostotic syndrome (CHS) [4]. Five unrelated Bullmastiff males between 5 and 9 months old had asymmetrical bony proliferation of the frontal, temporal, and occipital bones, with one dog having bony proliferation of the tympanic bullae[4]. All dogs with CHS recovered. Trowald-Wigh reported 12 Irish setters with confirmed canine leucocyte adhesion deficiency (CLAD) [23]. The pathogenesis of CLAD includes absence of granulocyte adhesion proteins and the inability of neutrophils to migrate from blood vessels into the tissues [23]. Similar diseases have been reported in humans and bovines [23]. CMO-like lesions were reported; however, CLAD lesions also include various osteopathies of long bones, purulent infections, and multi-organ involvement. These 12 Irish setters with CLAD were between 8 weeks and 15 weeks old at the onset of clinical signs, and all were euthanized owing to the severity and recurrence of clinical signs [23]. Two litters each had 4 CLAD dogs, the remaining 2 were unrelated [23].

Etiology

CMO’s etiology is unknown [1,27-31]. Etiologies considered include congenital [1,25] and infectious [21,26], and inherited [1,25]. Neither case histories nor the literature indicate that CMO is present at birth, which by definition means it is not a congenital disease [27]. Rather, CMO ostensibly develops at 3 to 9 months of age (Fig. 96-1).

Infection does not appear to be the cause of CMO. Microscopic evaluation of affected tissues does not show infectious organisms. Bacterial cultures (n=26) from 4 West Highland white terriers were negative [22]. Antibiotics used in CMO cases have not be reported as an effective treatment [1-31]. Schulz reported E. coli was cultured from a boxer’s mandible affected with CMO [13], which was probably incidental. The predominance of CMO cases occurring in terriers, especially West Highland and Scottish, strongly suggest a genetic etiology. Conversely, CMO occurring in multiple other breeds, including some large breed dogs, causes some doubt regarding a genetic etiology, assuming these other breeds were pure bred and that CMO was not confused with a similar disease.

Figure 96-1. The VMDB does not give number of cases at every month, or year, of age. Cases within an age range are reported as "0-2 wks; 2 wks-; 2 mn; 2-6 mn; 6-12 mn; 1-2 yr; 2-4 yr; 4-7 yr; 7-10 yr; 10-; 15 yr; and 15 yr+". The number of cases for VMDB data in Figure 96-1 was placed at the center of the age ranges, with cases ≥4 years old placed at 60 months on the chart. 8 West Highland terriers with CMO reported by Riserx did not report age, but were included in breed assessments.

Pathology

Normal lamellar bone is removed by osteoclasts and may be accompanied by massive numbers of inflammatory cells (predominantly lymphocytes, plasma cells, and neutrophils). Muscle and connective tissue along the normal bone surface are also destroyed by this pathologic process. New bone formation is coarse and/or woven, and extends well beyond the normal periosteum. The marrow spaces are filled with highly vascular fibrous tissue, and occasionally, islets of cartilage. The new bone can have a "mosaic pattern...indicating the sporadic and rapid deposit and resorption of the abnormal bone" [1]. Similar pathologic changes can be observed with some osteosarcomas, hyperparathyroidism, and callous formation [1]. The pathologic changes vary with the bone involved. Mandibular changes are characterized by large, irregular exostosis, whereas changes of the calvarium and tympanic bullae most often result in thickening while maintaining a relatively smooth inner and outer surface [1].

Gross changes are readily apparent, especially of the mandibles (Fig. 96-2). Visible and palpable enlargement of the mandibles is hallmark for CMO. Bilateral symmetry is the rule, but there are many exceptions. The tympanic bullae are usually involved, with enlargements by 2 to 3 times normal size caused by massive amounts of new bone [1]. In addition, variable amounts of fusion between the enlarged tympanic bullae and the angle of the mandible are common [1].

Figure 96-2. Gross bony changes owing to CMO. Note the large amount of irregular bony proliferation of the mandibles. In some cases, the tympanic bullae, temporomandibular joint, and flat bones of the calvarium may also be affected.

Clinical Diagnosis

Signalment

The quintessential case of CMO is an intact male Scottish terrier or West Highland white terrier up to 12 months old.

Age

Dogs aged up to 12 months accounted for 82% of the cases in our VMDB survey (Fig. 96-2). The age range was from 0 to 2 weeks to 15 years old (one dog in each) (Fig. 96-1). CMO is generally considered a juvenile disease, with cessation of clinical signs with osseous maturity. Because similar pathologic changes can be observed with some osteosarcomas, hyperparathyroidism, and callous formation [1], misdiagnosis is a possibility for the 5 mature dogs indicated to have CMO out of a total population over 300,000 dogs.

The age of the 65 dogs with CMO reported in the literature ranged from 3 months to 13 months old at presentation, plus 1 dog at 24 months old with bone proliferation of the frontal sinus and polyarthritis [4-24].

Breed

West Highland white terriers and Scottish terriers were by far the most common breeds to have CMO, and had the greatest risk per 100,000 of the breeds (Table 96-1). Although West Highland white terriers had the most cases of CMO, Scottish terriers had the highest risk based on number of CMO cases per 100,000 of the breed. Mixed breed dogs had the lowest number of cases (n=2) and the lowest risk (2 CMO cases/100,000 mixed breed dogs). However, the risk for CMO overall was low, as indicated by only 9 CMO cases per 100,000 of all breeds. In addition, the low number of CMO cases per 100,000 for the breeds at highest risk was also low compared with risk factors for other diseases (i.e., hypertrophic osteodystrophy and panosteitis). Terriers accounted for 16 of the 29 CMO cases (55%) reported in the literature [4-24]. However, large breed dogs such as the bulldog, Bassett Hound, Weimaraner, Bullmastiff and Great Dane were also reported to have had CMO (Table 96-1) [4-24].

Gender

Males are more likely to have CMO based on the VMDB survey for this chapter (Table 96-2). The male:female ratio was 48:52 for all dogs, while those with CMO had a male:female ratio of 64:36. A strong predilection appears to exist for intact dogs to have CMO (85%) (Table 96-2). However, the vast majority of dogs with CMO were 12 months old or younger, and for all dogs up to 12 months old the percentage of intact dogs (76% of males and 69% of females) was closer to the percentage of dogs with CMO that were intact.

Patient History

CMO has an insidious onset. The dog’s presenting complaint(s) are most often pain when a person opens the dog’s mouth and decreasing ability to open the mouth (decreased range of motion of the temporomandibular joint). More advanced cases also have visible enlargement of the mandible, decreased eating, and perhaps weight loss. Other dogs of that litter may also be affected.

Examination Findings

The presenting complaints are confirmed. Palpation of the mandibles can reveal an irregular surface and enlargement. The animal has pain on attempting to open the mouth and an inability to open the mouth to a normal width even with sedation/anesthesia. A complete examination should be performed to rule out retrobulbar abscess, fracture, and oral lesions (e.g., tooth disease, foreign body, etc.).

Radiographic Findings

Enlargement of the mandibles is the earliest and most obvious radiographic abnormality (Fig. 96-3) and may be extreme in advanced cases. Enlargement of the tympanic bullae is predominantly via thickening of the bony wall and may be several times normal size. Radiodensity and/or bone proliferation between the tympanic bullae and the angle of the mandible may be observed. Flat bones of the calvarium (especially the frontal and parietal bones) may be markedly thicker, but tend to maintain smooth cortical surfaces.

Figure 96-3. Radiographs of CMO. Note the large amount of bony proliferation of the mandibles. The tympanic bullae, temporomandibular joint, and flat bones of the cranium may also be involved in some cases.

Treatment

Corticosteroids titrated against the clinical signs are the primary treatment for CMO. Various analgesics have also reportedly been used for pain control; however, aspirin has been specifically and repeatedly reported to be ineffective. Antibiotic use has been reported infrequently and shown to be without notable effect. Soft, high-caloric diets are indicated to decrease the pain associated with eating and to maintain body weight. Supportive care, especially fluids and caloric supplementation, may be necessary. Physical therapy aimed at maintaining temporomandibular range of motion has not been reported, but could potentially be beneficial.

Prognosis

Outcome of the disease in 42 dogs has been reported in the literature. Thirty (30) dogs survived, ostensibly with resolution of the CMO lesions. Age at resolution was given in only one dog, at 11 months old [5]. Five dogs with CMO were euthanized [6-9]. Two dogs died, one during the first night of hospitalization and the other after 9 weeks of treatment [10,14]. Fourteen other dogs had follow up examinations between 10 weeks and 9 years after initial treatment, and had lesions that were ostensibly either resolved or resolving [6,8-13]. Insufficient information exists to determine whether prognosis is related to age at onset, age at which treatment begins, severity of clinical signs at the time of initiating treatment, speed of progression of clinical signs, or other factors.