Panosteitis

What it is

Panosteitis (also called eosinophilic panosteitis or enostosis) is a self-limiting disease of unknown cause that affects the bone marrow cavity of the long bones. The fatty marrow undergoes degeneration and fibrosis, and woven bone forms inside the medullary cavity, later also under the periosteum. Over weeks to months the new bone is remodelled and the marrow returns to normal. Genetic factors are suspected; diet, infection and immune mechanisms have been proposed, but none is proven.

Who it affects

Young dogs of medium, large and giant breeds, usually between 5 and 18 months of age, although it can appear up to about 2 years and occasionally later. The German shepherd is the classic breed; basset hound, Labrador and golden retriever, Rottweiler and Dobermann are also affected. Males are affected more often.

Anatomy involved

The lesions start near the nutrient foramen of the diaphysis and spread through the medullary cavity. The bones most often involved are the ulna, radius, humerus, femur and tibia; several bones and several limbs are usually involved, at different times.

Clinical signs

Sudden lameness without a history of trauma that may shift from one limb to another (shifting leg lameness) and recur in episodes over months. The key sign is pain on deep palpation of the diaphysis of the affected bone, away from the joints. Some dogs show lethargy, inappetence or fever during episodes.

Diagnosis

• Radiographs of the painful bone: patchy, ill-defined increases in medullary opacity, starting near the nutrient foramen, with blurring of the trabecular pattern; later, smooth periosteal new bone. Radiographic changes may lag behind the signs, and early lesions may not be visible.
• Rule out other causes of lameness in growing dogs: elbow dysplasia, osteochondrosis, hypertrophic osteodystrophy, trauma.

Treatment

The disease resolves on its own, usually by the end of skeletal maturity. Treatment controls pain: NSAIDs or other analgesics during episodes and reduced exercise. Prognosis is excellent, but owners should know that new episodes in other bones are common until the dog stops growing.