Spinal muscle pathology.

Clinical signs that are easily referred to spinal muscle pathology include atrophy of epaxial muscles, focal swelling and palpable tenderness, as well as enlarged muscles with increased tone. Less easily recognized signs include rigidity of the spine, shortened stride, hindlimb lameness, and indicators of poor performance. Muscle biopsy is one option in evaluating sore backs and is best used when physical examination and imaging procedures do not reveal a likely diagnosis or when conventional treatments are unsuccessful. Rhabdomyolysis of spinal muscles may be due to nutritional myodegeneration (foals), recurrent exertional rhabdomyolysis, and polysaccharide storage myopathy. Atrophy of spinal muscles can be due to severe rhabdomyolysis, immune-related myopathy, or neurogenic atrophy from nerve trauma, EPM, or EMND.