title: Immune-Mediated Muscle Diseases of the Horse.
abstract: In horses, immune-mediated muscle disorders can arise from an overzealous immune response to concurrent infections or potentially from an inherent immune response to host muscle antigens. Streptococcus equi ss. equi infection or vaccination can result in infarctive purpura hemorrhagica (IPH) in which vascular deposition of IgA-streptococcal M protein complexes produces ischemia and complete focal infarction of skeletal muscle and internal organs. In Quarter Horse-related breeds with immune-mediated myositis, an apparent abnormal immune response to muscle antigens results in upregulation of major histocompatibility complex class (MHC) I and II on muscle cell membranes, lymphocytic infiltration of lumbar and gluteal myofibers, and subsequent gross muscle atrophy. Rarely, an inflammatory event results in myositis with subsequent systemic calcinosis characterized by a pathognomonic hyperphosphatemia and high fatality rate. This review presents an overview of these immune-mediated myopathies and highlights clinical and pathological features as well as the suspected pathophysiology.
authors.affiliation: 1 Department of Veterinary Population Medicine, College of Veterinary Medicine, University of Minnesota, St Paul, MN, USA.
authors.forename: S A
authors.initials: SA
authors.lastname: Durward-Akhurst
authors.affiliation: 2 Department of Large Animal Clinical Sciences, Michigan State University, East Lansing, MI, USA.
authors.forename: S J
authors.initials: SJ
authors.lastname: Valberg
mesh_terms: D000818:Animals; D001327:Autoimmune Diseases / Q000473:pathology / Q000662:veterinary; D006734:Horse Diseases / Q000276:immunology* / Q000473:pathology; D006736:Horses; D018482:Muscle, Skeletal / Q000276:immunology / Q000473:pathology; D009135:Muscular Diseases / Q000276:immunology / Q000662:veterinary*
keywords: horse; immunologic/inflammation; musculoskeletal; myositis