JPC SYSTEMIC PATHOLOGY
Signalment: Stillborn piglet of unknown gender
HISTORY (JPC #1810706): Tissue from 1 of 3 stillborn piglets, which had thickened forelegs.
HISTOPATHOLOGIC DESCRIPTION: Radius/ulna with adjacent skeletal muscle and tendons: Radiating diffusely and circumferentially from the surface of normal cortical bone and markedly elevating the overlying periosteum is a circumferential layer of trabecular bone up to 4 mm thick, and composed of thin, trabeculae of woven bone oriented perpendicular to the surface of the bone, and which lack normal bone marrow elements and are separated by loose fibromyxomatous connective tissue. Diffusely, the periosteum is markedly thickened up to 250 um by fibrous connective tissue, and the inner periosteal margin is lined by up to 5 layers of osteoblasts separated by variable amounts of osteoid. The connective tissue surrounding the trabeculae is sparsely vascular and contains numerous loosely and haphazardly arranged spindle to stellate cells and wispy fibrous connective tissue widely separated by clear space (edema). Connective tissue from the thickened, reactive periosteum merges and fuses with adjacent tendons and separates and surrounds markedly atrophied skeletal muscle. The connective tissue elements surrounding the periosteum are thickened and edematous. Surrounding skeletal muscle contains shrunken and atrophied myofibers and regenerative, multinucleated fibers, which are surrounded by edema. There is a focal area of periosteal mineralization, and multifocal mild scattered hemorrhage and perivascular edema.
MORPHOLOGIC DIAGNOSIS: Radius/Ulna: Periosteal new bone formation (hyperostosis), diffuse, severe, with edema and marked muscle atrophy, breed unspecified, porcine.
CONDITION: Congenital hyperostosis
SYNONYMS: Congenital porcine cortical hyperostosis, diaphyseal dysplasia, congenital thick foreleg, “thick legs”
- Hyperosteosis in general refers to excessive bone formation as nonspecific response to various forms of bone injury, i.e., trauma, infection, metabolic imbalance, etc.
- Congenital hyperostosis:
- Rare autosomal recessive congenital disease of newborn swine
- Excessive periosteal bone formation (thickened limbs) within long bones
- Axial skeleton not affected
- Radius and ulna are most severely affected
- Only cortical bone affected; growth plates and trabecular bone not involved
- Hypertrophic osteopathy syndrome: diffuse, periosteal new bone formation along the diaphysis and metaphysis of certain limb bones due to chronic inflammation or neoplasm, more common in thoracic cavity
- New bone growth is usually confined to limbs
- Characterized by hyperemia, edema, granulation of periosteum > osteoid deposition on existing cortical bone >trabecular bone
- Unknown; presumed to be an autosomal recessive trait
- Proposed pathogenesis:
- Local circulatory disturbance due to positioning in the uterus > extensive periosteal reaction; arteriosclerosis of small arteries and arterioles has been observed in vessels supplying the radioulnar region in affected pigs > disorganization of the perichondrial ossification groove of Ranvier (the chondrogenic membrane surrounding the growth plate enabling expansion of the growth plate)
TYPICAL CLINICAL FINDINGS:
- Piglets are either stillborn or die within the first days of life.
- One or both forelimbs are firm and enlarged; occasionally affects hindlimbs
- Overlying skin: Hyperemic, tense and fixed to underlying tissue
TYPICAL GROSS FINDINGS:
- Enlarged limbs up to twice normal diameter; thick layer of extracortical bone extends along the diaphysis of the radius, ulna and tibia
- Marked edema and swelling of surrounding soft tissues
- Normal joints and epiphyses
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Radiating spicules of woven bone extend from the surface of preexisting cortical bone, under a thickened periosteum; no intervening marrow; no evidence of excessive bone resorption or remodeling
- Bone spicules are oriented perpendicular to the long axis of the cortex and arise from the cambium layer of the periosteum
- Overlying thickened periosteum is lined by multiple layers of active osteoblasts; periosteum merges with surrounding edematous, poorly vascular connective tissue; merged tissues fuse with adjacent muscle and the overlying dermis
- Reactive periosteal hyperostosis secondary to infection, neoplasia, trauma, or metabolic disease
- Osteopetrosis: Thickening of spongiosa due to decreased osteoclast resorption
- Hypertrophic pulmonary osteopathy: Not found in neonatal animals and associated with inflammatory and neoplastic conditions in the thoracic cavity; characterized by periosteal new bone formation
- Humans: Resembles Caffey's disease in children (diaphyseal dysplasia, infantile cortical hyperostosis); human disease is self-limiting and regresses
- Dog: Craniomandibular osteopathy “lion jaw” most common in West Highland White terrier
- Also, seen in Scottish terrier, labrador retrievers, great danes, doberman pinschers, cairn terriers, German wirehaired pointers, and others
- Proliferative disorder mostly confined to bones of skull, particularly mandible, and occipital and temporal bones
- Seen microscopically as endosteum, periosteum, and trabecular bones
- Dog: Calvarial hyperostosis of Bullmastiffs: asymmetrical hyperosteosis of skull without involvement of mandible
- Non-human primates: Report in rhesus monkeys of a condition resembling Caffey’s disease
- 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. Philadelphia, PA: Elsevier; 2016: 53, 91-94.
- Decker S, Volk HA. Dorsal vertebral column abnormalities in dogs with disseminated idiopathic skeletal hyperostosis (DISH). Vet Rec. 2014;174(25):632.
- Doize B, Martineau G. Congential hyperostosis in piglets: A consequence of a disorganization of the perichondrial ossification groove of Ranvier. Can J Comp Med. 1984;48:414-419.
- Olson EJ, Carlson CS. Bones, Joints, Tendons, and Ligaments. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 6th ed. St. Louis, MO: Elsevier; 2017:1005-1007.
- Slovak JE, Gilmour LJ, Miles KG. What is your diagnosis? Idiopathic calvarial hyperkeratosis. J Am Vet Med Assoc. 2015 Jun 1;246(11):1187.
- Snook SS, King NW. Familial infantile cortical hyperostosis (Caffey's disease) in rhesus monkeys (Macaca mulatta). Vet Pathol. 1989;26(3):274-277.