The presenting symptoms of rhabdomyolysis are usually acute in onset and include myalgias, stiffness, weakness, malaise, low-grade fever, and dark (usually brown) urine. Symptoms relating to the musculoskeletal system, however, may be present in only 271 percent of cases.7 Nausea, vomiting, abdominal pain, and tachycardia can occur in severe rhabdomyolysis. On occasion, mental-status changes are present secondary to urea induced encephalopathy. Swelling and tenderness of the involved muscle groups and hemorrhagic discoloration of overlying skin may be observed, but only in a minority of cases. Muscle swelling may not become apparent until after rehydration with intravenous (IV) fluids. The muscle groups involved may be localized or diffuse, depending on the etiology. Commonly, the postural muscles of the thighs, calves, and the lower back are involved. An important point to remember is that acute rhabdomyolysis may be present without any of these signs or symptoms, and the patient may have essentially normal findings on physical examination. For this reason, the diagnosis is often made only after soliciting a historical clue (e.g., recent cocaine use) or finding an elevated serum CPK or the presence of myoglobinuria on routine laboratory testing.
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