Renal · Acute Kidney Injury
The facts most likely to be tested
The classic clinical triad of rhabdomyolysis consists of muscle pain, weakness, and dark tea-colored urine.
Laboratory diagnosis is confirmed by a markedly elevated creatine kinase (CK), typically exceeding 5,000 U/L.
Urinalysis will demonstrate positive blood on dipstick in the absence of red blood cells on microscopic examination, indicating myoglobinuria.
The most feared and life-threatening electrolyte complication is hyperkalemia, which can lead to peaked T-waves and cardiac arrhythmias.
Acute kidney injury occurs due to myoglobin-induced tubular necrosis and intratubular cast formation.
The first-line treatment is aggressive intravenous fluid resuscitation with isotonic saline to maintain high urine output.
Statin therapy, particularly when combined with fibrates or cytochrome P450 inhibitors, is a common iatrogenic cause of rhabdomyolysis.
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A 28-year-old male is brought to the emergency department after collapsing during a high-intensity marathon. He reports severe bilateral thigh pain and has passed a small amount of dark, tea-colored urine. Physical examination reveals tenderness to palpation of the quadriceps and decreased muscle strength. Laboratory studies show a creatine kinase level of 18,000 U/L and a serum potassium of 5.8 mEq/L. Urinalysis is positive for blood on dipstick, but microscopy shows 0-2 RBCs/hpf.
What is the most appropriate initial management for this patient?
Aggressive intravenous fluid resuscitation
The patient presents with classic signs of rhabdomyolysis; the most critical initial step is aggressive fluid resuscitation to prevent myoglobin-induced acute tubular necrosis.
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Etiology / Epidemiology
Caused by muscle trauma, statin use, or prolonged immobilization. High risk in crush injuries and extreme exertion.
Clinical Manifestations
Classic triad: muscle pain, weakness, and tea-colored urine. Look for dark brown urine without RBCs.
Diagnosis
Gold standard is serum creatine kinase (CK) >5,000 U/L. Urinalysis shows positive heme without RBCs.
Treatment
Aggressive IV isotonic saline resuscitation. Avoid potassium-containing fluids if hyperkalemia is present.
Prognosis
Major risk is acute kidney injury (AKI). Monitor urine output closely to prevent renal failure.
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Epidemiology & Etiology
Common triggers include crush injuries, seizures, and statin-fibrate combinations. Excessive physical exertion in hot environments is a frequent cause in military or athletic populations. Alcohol abuse and illicit drug use are significant predisposing factors.
Pertinent Anatomy
Skeletal muscle breakdown releases intracellular contents into the systemic circulation. The kidneys are the primary site of injury due to the filtration of myoglobin.
Pathophysiology
Muscle cell membrane disruption leads to an influx of calcium, causing sustained contraction and ATP depletion. This results in the release of myoglobin, potassium, and phosphate into the blood. Myoglobin is nephrotoxic, causing pigment nephropathy via tubular obstruction and direct oxidative stress.
Clinical Manifestations
Patients present with myalgias, generalized weakness, and tea-colored urine. Physical exam may reveal muscle tenderness or swelling. Hyperkalemia is the most life-threatening complication, potentially causing cardiac arrhythmias. Always assess for compartment syndrome in crush injuries.
Diagnosis
The serum creatine kinase (CK) is the most sensitive marker, typically rising >5,000 U/L. Urinalysis reveals positive heme on dipstick, but microscopy shows no RBCs, indicating myoglobinuria. Monitor serum creatinine and electrolytes for signs of renal impairment.
Treatment
Initiate IV isotonic saline immediately to maintain high urine output (200-300 mL/hr). Avoid potassium-containing fluids and nephrotoxic agents like NSAIDs. If hyperkalemia is present, treat with standard cardiac stabilization and potassium-lowering protocols.
Prognosis
The primary complication is acute kidney injury (AKI), which occurs in up to 30% of cases. Monitor urine output and electrolytes until CK levels trend downward. Severe cases may require hemodialysis if refractory hyperkalemia or fluid overload develops.
Differential Diagnosis
Myocardial Infarction: elevated troponin without muscle pain
Acute Kidney Injury: elevated creatinine without myoglobinuria
Hemolysis: positive heme with RBCs on microscopy
Compartment Syndrome: tense, painful limb with normal CK
Polymyositis: chronic weakness with lower CK levels