Non-exertional myopathies (Proceedings)
Characterized by clinical and laboratory findings of muscle damage not associated with exercise. Includes inflammatory, nutritional, toxic, traumatic, metabolic, congenital, immune mediated and idiopathic causes of muscle disease.
Inflammatory myopathies: Myopathy related to infectious agents or immune mediated damage.
• Clinical signs: In horses: usually arises at IM injection sites (80% of cases), but can develop in regions of muscle trauma and in open wounds. Clinical signs arise within 48 hours. Firm, hot, swollen and painful area often with crepitance. Tachycardia, tachypnea, fever and lameness are common. Complications include IMHA, coagulopathies and laminitis. Clostridium septicum and Clostridium perfringens are the most frequently isolated organisms in horses.
• Lab findings: elevated CK and AST (usually mild), CBC consistent with toxemia and inflammation.
• Diagnosis is based on clinical signs, ultrasonography (fluid pockets, gas production, edema), cytology of aspirated fluid (large gram positive rods) and the growth of Clostridia on anaerobic culture.
• Treatment: Penicillin and/or metronidazole. Surgical debridement and wound flushing. Initial antibiotic treatment is aggressive (penicillin 44 000 IU/kg every 2 to 4 hours until the animal is stable)
• Adjunct therapy: anti- inflammatory drugs, IV fluids, analgesia, hydrotherapy, topical wound therapy, fly control.
• High mortality rate (~ 68%), so early and aggressive therapy is critical. Infections with Cl. septicum are associated higher mortality rate than Cl. perfringens (85% vs. 25%). Cl. sordelli invariably fatal.
• Prevention: no licensed equine vaccine.