Exertional rhabdomyolysis occurs when skeletal muscle breaks down during excessive, repeatitive, and unfamiliar exercise. The severe and unaccustomed exercise stretches the cell membrane, increases its permeability, and leads to the release of myoglobin, creatine kinase, and other harmful proteins into the patient's blood. Severe rhabdomyolysis results in renal failure in 5-7% of cases as myoglobin accumulates in the patient’s blood, spills into their urine, and create deposits (casts) that block the renal tubules and restrict renal blood flow. Death is rare but possible. Dehydration and heat stress exacerbate the condition, especially in unacclimatized individuals. People with Sickle Cell Trait* and those with some metabolic disorders are predisposed to the "rhabdo." Wildland firefighters and those engaging in heavy exercise in similar conditions are at risk, especially during their initial training.
*People with Sickle Cell Trait (SCT) inherit the sickle cell gene from one parent and while they do not typically present with the signs and symptoms of Sickle Cell Disease, they are a carrier. Over three million Americans have SCT.
Patients with exertional rhabdomyolysis will present with a history of strenuous exercise, often in a moderate to severe heat challenge, severe, often incapacitating muscle pain, and unusually dark urine. In combination, these indicate the need for immediate assessment by a physician. Myoglobin in the urine (myoglobinuria) can be confirmed via a simple urine dipstick test, a positive test indicates testing for high levels of creatine kinase (CK) a muscle enzyme released with myoglobin when skeletal muscle is damaged. CK levels 5-20 times greater than normal are common with exertional rhabdomyolysis.
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