Inflammatory and Immune-Mediated Muscle Disorders

A suspicion of inflammatory myopathy in horses arises from clinical history, physical exam findings, hematologic findings, serum biochemistry profile, and bacterial cultures/PCR or serum titers. In horses, inflammatory myopathies are not as well characterized, and it is difficult to clearly discern whether myositis arises as a secondary consequence of an infection, or represents a primary immune-mediated disorder. Nevertheless, for the purposes of stimulating more thought with regard to immune-mediated disorders in horses, this chapter includes inflammatory myopathies linked to the immune response to concurrent infections (e.g., infarctive purpura hemorrhagica (IPH), Streptococcus equi rhabdomyolysis) and those likely triggered by autoimmunity or an aberrant immune response (e.g., immune-mediated myositis in Quarter Horse-related breeds, systemic calcinosis, inflammatory/immune mediated myositis, and sarcoystis myositis).