Hypertrophic osteodystrophy

Speculated causes of HOD

Proposed causes include decreased Vitamin C uptake, excessive mineral and vitamin supplementation, and infection with canine distemper virus (CDV). Decreased Vitamin C uptake has been dismissed, but excessive calcium supplementation remains a possibility.

Over-feeding is not considered a significant cause. In Weimaraners, recent vaccination with a modified live vaccine, particularly for canine distemper, has been suspected due to symptom overlap and temporal association, though no definitive link has been proven. Familial clustering in Weimaraners suggests a genetic or partly genetic origin.

Clinical features

Lameness is the primary characteristic, resulting from swelling of the metaphysis of long bones; other affected bones may include ribs, metacarpals, mandible, and scapula. Lameness ranges from mild limping to inability to stand, and some puppies adopt a cow-hocked stance or a roached spine. Pain on palpation, limb warmth, depression, and loss of appetite accompany the lameness.

Limb involvement is usually bilateral and episodic; most dogs recover after one episode, but some relapse. Systemic manifestations—fever, multiple organ inflammation, nasal and ocular discharge, diarrhea, foot pad hyperkeratosis, pneumonia, and tooth enamel hypoplasia—indicate a poorer prognosis. Early diagnosis relies on clinical signs after ruling out other disorders.

Radiographic features

Diagnosis depends on clinical signs and characteristic radiographic changes in the metaphyses. Early radiographs show an uneven radiolucent zone parallel to the physis with a thin band of increased radiodensity bordering the physis, sometimes described as moth-eaten.

As the disease progresses, the radiolucent line may disappear and radiodensity increases as repair occurs. Relapses can produce new radiolucent lines. A dark line at the metaphysis may appear, followed by new bone growth externally, representing microfractures and periosteal bridging.

Treatment

Mild cases are often managed with NSAIDs and supportive care. For severe systemic symptoms unresponsive to NSAIDs, the Weimaraner and Irish Setter AKC parent clubs advocate immunosuppressive doses of corticosteroids, supplemented with antibiotics and antacids to protect the stomach lining. More severe cases require IV fluids, electrolytes, nutritional support, and intensive nursing. Vitamin C supplementation is contraindicated because it may raise blood calcium levels and worsen the disease.