Myositis ossificans is an idiopathic proliferation of fibrovascular tissue in the muscle, with secondary calcification and ossification. This degenerative myopathy affects young-adult to middle-aged dogs and cats of both sexes.
Clinical signs of myositis ossificans can include the following:
progressive weakness and stiffness of gait
enlargement of proximal limb muscles
myalgia
focal, firm swellings on palpation
Diagnosis is based on signalment, clinical signs, and radiographic evidence of mineralized or ossified densities (usually multiple) within muscle tissue. Serum CK activity is typically elevated, and electromyographic findings are abnormal.
Treatment for myositis ossificans is indicated only for major lesions. Surgical removal of the ossified portion of the affected muscle may be considered if the lesion is painful or limits joint movement.
The prognosis for dogs and cats with myositis ossificans is guarded to poor, as this is a progressive disease; however, focal lesions may regress or respond positively to surgical excision.
For other degenerative/developmental myopathies in dogs and cats, see the Overview for this chapter.
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Also see pet owner content regarding myositis ossificans in dogs.
