Acute necrosis of skeletal muscle fibers and leakage of cellular contents into circulation.
MCC: alcohol (chronic alcoholics also have deficits in hypokalemia/hypomagnesium/hypophosphatemia which can exacerbate) as well as drugs of abuse (cocaine, PCP, LSD, amphetamines). 3 categories: traumatic (crush injuries), non-traumatic exertional (marathoners), non-traumatic non-exertional (drugs)
Other drugs: antipsychotics, lipid-lowering agents (statins, chofibrate), SSRIs, zidovudine, colchine, lithium, antihistamines, narcotics.
Infectious causes: influenza, legionella
Myalgias, stiffness, weakness, malaise, low-grade fever, dark urine. Swelling/tenderness to involved muscle groups though can be localized or diffuse (postural muscles common: thigh, calves, lower back).
Elevated CK correlates with amount of muscle injury and severity of illness though does not correlate with chances of renal failure or mortality. Usually 5x normal range. Rises 2-12 hours after vent, peaks at 24-72 hours, then drops at about 40% per day afterward.
Myoglobin rises before CPK. Contains heme so urine dipstick will be positive though negative RBCs. About 20% of rhabdo will have myoglobinuremia (Alhedi, 2014). Very specific, though not very sensitive.
BUN/Cr will be lower likely less than 10 due to elevated creatinine rise with muscle breakdown. Look for elevated potassium/phosphate due to muscle cell breakdown.
Complications include DIC, elevated LFTs, renal failure (obviously)
IV fluids is the maintain of therapy. NS > LR. Need urine output at 250cc/hr if admitted.
Urine alkalization (theory is myoglobin which typically causes the nephrotoxicity is worse in acidic environment; sodium bicarb 1amp/1 NS L at 100cc/hr), diuretics, mannitol have no benefit in the ED (or likely at all).
Healthy patients with exertional rhabdo with no co-morbidites can be discharged after oral and IV fluids. Paper looking at patients at risk for severe renal failure only showed if initial creatinine > 1.7 was only true RF (Fernandez, 2005). Also consider >6000 and continuing to trend upward.
Tintinalli, Seventh Edition, Chapter 92: Rhabdomyolysis
EMCAST, November 2009