Myopathies

This chapter deals with myopathies in dogs and cats. It discusses etiology/pathophysiology, epidemiology, signalment, history and clinical signs, diagnosis, therapy, and prognosis of myopathies. Myopathies occur secondary to either intrinsic pathology within the myofiber itself (noninflammatory myopathy) or infiltration and damage by inflammatory cells (myositis) from infectious or immune-mediated disease. About one-third of canine generalized inflammatory myopathies (myositides) are associated with infectious agents, although a causal relationship will be difficult to determine unless histopathologically confirmed. Functional manifestations of myopathies may include gait abnormalities (lameness, stiff or stilted gait), exercise intolerance, and focal or generalized weakness. Isolating the problem to a myopathic process typically requires a combination of serologic, functional, and histologic evaluation of the muscle. Therapy consists of nutritional supplementation with L-carnitine, co-enzyme Q10, and vitamin B complex for many noninflammatory myopathies. If an infectious etiology is identified on biopsy or suspected clinically, appropriate antimicrobial therapy should be instituted.