Predispositions for exertional rhabdomyolysis include: a high protein and high carbohydrate diet unaccustomed exercise selenium-vitamin E deficiency potassium deficiency systemic viral infection nervous disposition stressful situations
It is reported that exertional rhabdomyolysis is seen more in mares than in geldings or stallions which may indicate a link to hormone imbalances. It is also reported that Quarter horses, Thoroughbreds and Standardbreds have a higher incidence of exertional rhabdomyolysis than other breeds. This may be related to genetic predisposition or may have a relation to the type of exercise those breeds are most often involved in. Recently links to equine polysaccharide storage myopathy, have been illustrated in studies done primarily on Quarter horses. acid in the extracellular space surrounding muscle cells. When lactic acid builds up it causes a drop in the local pH which causes localized vasoconstriction, ischemia and hypoxia of the muscle cells. Hypoxic damage causes muscle cells to and may cause some cells to lyse. The lysis of muscle cells releases digestive enzymes that attack the surrounding muscle cells. The result is massive, localised . One theory on the pathogenesis of exertional rhabdomyolysis is the build up of The damage is usually restricted to muscle groups containing high amounts of type muscle fibres as these fibres have a high capacity for anaerobic glycolysis, and therefore produce higher quantities of lactic acid, but secondary damage may occur in the as these organs filter and remove muscle enzymes form the blood. Another theory of the pathogenesis of exertional rhabdomyolysis involves many of the same mechanisms but does not rely on hypoxic damage as the cause of the initial lysis of muscle cells. In this theory any situation that causes the rupture of muscle cells may lead to the release of digestive muscle enzymes that cause massive, localized myolysis. Injury such as strain, direct trauma, or unaccustomed overuse of a muscle may be the triggering event for the onset of exertional rhabdomyolysis. Exertional rhabdomyolysis is clinically characterized by the sudden onset of , fasciculation, spasm and weakness of the muscles of the back and hindquarters during, or immediately following, intense exercise. The horse tends to have a stiff gait, is reluctant to move, or has reduced performance depending on the severity and extent of muscle damage. Sweating and increased TPR commonly accompany episodes of exertional rhabdomyolysis. There is pain on palpation of affected muscles and those muscles feel hypertonic or spasmodic. In severe or repeated cases horses may experience myoglobinurea, dysuria or anuria, which is indicative of kidney damage.
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