JPC SYSTEMIC PATHOLOGY
MUSCULOSKELETAL SYSTEM
March 2022
M-M18

 

Signalment (JPC #1712510):  Dog

 

HISTORY:  None

 

HISTOPATHOLOGIC DESCRIPTION:  Bone, mandible (per contributor) with tooth, gingiva, and skeletal muscle:  Diffusely the mandible is markedly thickened by a subperiosteal / endosteal proliferation of trabecular bone that effaces the cortex and creates an undulant bone surface. The subperiosteal trabeculae are arranged perpendicularly to the periosteum, are composed primarily of woven bone interspersed with rare areas of lamellar bone, are often moderately increased in thickness (osteosclerosis), and are often widely separated by variably dense areas of fibrosis.  Trabeculae contain many resting and reversal lines and are often lined by many osteoblasts and fewer osteoclasts within Howship’s lacunae (remodeling). The periosteum is expanded 1 to 5 mm thick by dense, fibrous connective tissue (fibrosis).    Within a focally extensive area, numerous neutrophils and admixed hemorrhage surround fragmented, subperiosteal trabeculae and extend into the overlying periosteal fibrous connective tissue.  Multifocally, atrophic skeletal myofibers are entrapped within the expanded periosteum. 

 

MORPHOLOGIC DIAGNOSIS:  Bone, mandible (per contributor):  Subperiosteal new bone growth, diffuse, moderate, with focal acute neutrophilic osteitis, multifocal osteosclerosis, marked periosteal fibrosis, and skeletal muscle atrophy, breed unspecified, canine.

 

CONDITION:  Craniomandibular osteopathy

 

SYNONYM:  Lion jaw

 

GENERAL DISSCUSSION:

• Craniomandibular osteopathy is a bilateral, generally symmetrical, nonneoplastic proliferation of periosteal new bone with intermittent and concurrent bone formation and resorption that most commonly affects West Highland white, but is also described in other breeds including Scottish terriers, cairn terriers, Labrador Retrievers, and Great Danes.
• Primarily affects mandible, tympanic bullae, and occipital and temporal bones; occasionally affects parietal, frontal, maxillary, and lacrimal bones and rarely the appendicular skeleton
• Tympanic bullae are often severely affected
• Mandibular changes affect the endosteum, periosteum, and trabecular bone
• Initial presentation at 4 to 7 months of age

 

PATHOGENESIS:

• Pathogenesis is unknown, but likely multifactorial
• Infectious etiology is suggested by the presence of inflammatory infiltrates; no agent has been identified
• Prevalence in certain breeds implies a genetic basis; autosomal recessive inheritance is suggested in West Highland white and Scottish terriers
• Has been associated with a leukocyte adhesion molecule deficiency in a colony of Irish setter puppies with concurrent metaphyseal osteopathy
• Intermittent and progressive; self-limiting (lasting many weeks to a few months); may completely recede and is typically nonfatal
• Growth plates are not involved; resolution corresponds with growth plate closure
• Extensive ossification of the soft tissues surrounding the mandibular angular process may result in an inability to eat and may necessitate euthanasia

 

TYPICAL CLINICAL FINDINGS:

• Painful and difficult mastication
• Mandibular pain and swelling
• Fever

 

TYPICAL GROSS FINDINGS:

• Bilaterally symmetrical, extensive proliferation of bone; rarely asymmetric or unilateral
• Bone is thickened through the width and length of the mandible; greatest changes occur at angular process
• Ossification of soft tissues
• Atrophy of mastication muscles
• Tympanic bullae are filled with bone and often enlarged up to 2-4 times normal

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Changes in the endosteal and trabecular bone characterized by both bone resorption and formation with many reversal cement and resting lines within bony trabeculae
• Medullary spaces contain irregular, sclerotic trabeculae of woven bone often oriented perpendicular to cortex, separated by fibrous connective tissue which may fill marrow spaces
• The periosteum may also be thickened by fibrous connective tissue
• Random, disoriented osteoclastic resorption involving lamellar and woven bone with production of abundant coarsely woven bone
• Increased osteoblastic activity on trabecular surfaces
• Lymphocytes, plasma cells, and neutrophils often present in areas of remodeling and ossification
• Rarely osteonecrosis
• Resolution of the disease involves replacement of woven trabeculae with lamellar bone and gradual resorption

 

ADDITIONAL DIAGNOSTIC TESTS:

• Radiology: Generally symmetrical enlargement of mandibles and tympanic bullae

 

DIFFERENTIAL DIAGNOSIS:

• Calvarial hyperostosis syndrome: Progressive, self-limiting, asymmetrical thickening of calvaria; mandibles not involved; affects young (less than 1 year), male Bullmastiffs
• Metabolic: Renal and nutritional secondary hyperparathyroidism (fibrous osteodystrophy, M-M10)
• Neoplastic bone disease
• Dissecting periostitis

 

COMPARATIVE PATHOLOGY:

• Humans:
  • Infantile cortical hyperostosis (Caffey-Silverman syndrome): Bilateral proliferative bone disease of infants affecting the mandible
  • Paget's disease: Similar mosaic pattern of resting and reversal lines; paramyxoviral infection suggested as the etiology
• Swine:
  • Porcine congenital hyperostosis (M-M05): Primarily affects long bones in young animals
• Dogs:
  • Hypertrophic osteopathy (M-N05, formerly known as hypertrophic pulmonary osteopathy): Diffuse periosteal new bone formation most often in the distal radius, ulna, tibia, metacarpals or metatarsals associated with inflammation or neoplasia in the thorax
  • Canine hepatozoonosis ( americanum) may cause a similar lesion to hypertrophic osteopathy but generally occurs more proximal on the limb

 

REFERENCES:

1. Craig LE, Dittmer KE, Thompson KG. Bones and joints. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 1. 6th ed. St. Louis, MO: Elsevier; 2016:91-92.
2. Pastor KF, Boulay JP, Schelling SH, Carpenter JL. Idiopathic hyperostosis of the calvaria in five young bullmastiffs. J Am Anim Hosp Assoc. 2000; 36(5):439-445.
3. Thornburg LP. Infantile cortical hyperostosis (Caffey-Silverman syndrome). Animal model: Craniomandibular osteopathy in the canine. Am J Pathol. 1979; 95(2):575-578.
4. Olson EJ, Carlson CS. Bones, joints, tendons, and ligaments. In: McGavin MD, Zachary JF, eds. Pathologic Basis of Veterinary Disease. 6th ed. St. Louis, MO: Elsevier; 2017: 1006, 1261.
5. Woodard JC. Skeletal system. In: Jones TC, Hunt RD, King NW, eds. Veterinary Pathology, 6th ed. Baltimore, MD: Williams and Wilkins; 1997:913-914.

Click the slide to view.

---