| Clostridial myositis (also known as malignant edema) is an infrequent but serious life-threatening complication associated with injections. It will occurr at routine intramuscular (in the muscle) sites, inadvertent perivascular (outside a vein or artery) injection, surgical sites, wounds, or lacerations. A variety of commonly injected drugs have been associated with the occurrence of Clostridial myositis including flunixin meglumine (Banamine), B-vitamins, antihistamines, diopyrone, dexamethasone, selenium, epinephrine, vaccines, furosamide (such as Lasix), and dextrose. The technique of the injection or the way in which the wound occurred has not been demonstrated to influence the development of the disease. Therefore it is not clear whether Clostridial organisms are introduced through the skin or if Clostridial organisms are present within the muscle. In a recent report, investigators found no evidence of Clostridial organisms on cultured skin swabs. However, they did isolate dormant (inactive) spores within normal healthy skeletal muscle. Investigators theorize that Clostridial organisms gain access to the circulating blood through the gastrointestinal tract where the organism is commonly found. The Clostridial organisms then become embedded in normal skeletal muscle. An inflammatory response associated with either an injection or trauma from a wound begins a series of events within the muscle, creating an anaerobic (lack of oxygen) environment, which in turn activates Clostridial spore formation. Horses suffering from Clostridial myositis develop rapidly spreading areas of subcutaneous emphysema (air under the skin) within 6 – 72 hours following an injection or wound. Due to the severe pain associated with the muscle swelling a majority of horses are referred to the hospital for colic or for rhabdomyolysis (tying-up). However, the presence of a high temperature, reluctance to move, dehydration, elevated heart rate, and the almost pathoneumonic (diagnostic) sign of severe coldness of skin overlying the involved area along with a history of a recent injection or wound leads to the diagnosis of Clostridrial myositis. Laboratory analysis typically demonstrates highly elevated muscle enzymes such as AST (aspartate aminotransferase) and CK (creatine kinase). Immediate treatment includes high frequent doses of the intravenous antibiotics penicillin and metronidazole, shock volumes of intravenous fluids, intravenous non-steroidal anti-inflammatories (flunixin meglumine), intensive care monitoring and surgical fasciotomy. Fasciotomy (surgical splitting of the affected muscle) at the affected site is critical to improve oxygenation to the area thereby killing the Clostridrial organisms. Repeated fasciotomy may be required depending upon the site of involvement and the virulence of the organism. Left untreated, horses afflicted with Clostridrial myositis will rapidly and aggressively progress to death. |
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