Rhabdomyolysis
Formal Definition
Rhabdomyolysis — a clinical syndrome of skeletal muscle breakdown with release of intracellular contents (myoglobin, creatine kinase/pap, potassium, phosphate, urate) into systemic circulation, causing characteristic features including markedly elevated CK (often >5,000 U/L, can exceed 100,000), myoglobinuria (cola-colored urine), electrolyte derangements (hyperkalemia, hyperphosphatemia, hypocalcemia early), and risk of acute kidney injury (myoglobin-induced tubular injury and obstruction); common causes include trauma/crush injury, prolonged immobilization, exertion, drugs (statins, cocaine), genetic myopathies, infections, and inflammatory myopathies.
How It's Used on the Ward
"Rhabdo" — the muscle-melting syndrome that occurs after prolonged down-time (found down, marathon running, severe exertion), crush injuries, prolonged seizures, severe ischemia (compartment syndrome), or with drug toxicity (statins, daptomycin, colchicine); characterized by dark cola-colored urine ("myoglobinuria") and a CK climbing into the tens of thousands; can quickly cause AKI and electrolyte catastrophe if not aggressively fluid-resuscitated.
Example
""36-year-old man found down on his apartment floor after an unknown duration following weekend meth use. Brought in by EMS with left thigh swelling, severe pain on palpation, dark brown urine. Vitals: T 38.0, HR 124, BP 96/62, RR 24. Labs: CK 84,000 U/L, K 6.4, Cr 2.6 (baseline 0.9), urine myoglobin positive, urine dipstick blood-positive without RBCs. Diagnosis: rhabdomyolysis with crush myopathy from prolonged immobilization. Started on aggressive IV crystalloid (LR at 500 mL/hr), bicarbonate-containing fluids, K-lowering measures, urine output goal ≥300 mL/hr. Admitted to ICU for monitoring; CK trending down over 4 days, renal function normalizing.""
Clinical Context
Diagnostic criteria: typically CK >5× ULN (often >1,000 U/L minimum threshold for clinical concern; >5,000 U/L marks significant rhabdo); presence of myoglobinuria (dark urine, dipstick positive for blood without RBCs on microscopy); clinical scenario consistent with muscle injury. Causes: (1) Traumatic — crush injury, prolonged immobilization (found down, intoxicated, post-ICU comatose). (2) Exertional — severe exercise, seizures, severe asthma attacks. (3) Drugs/toxins — statins (higher risk with fibrates, CYP interactions), cocaine, meth, alcohol, daptomycin, colchicine. (4) Genetic — McArdle disease, CPT II deficiency, malignant hyperthermia. (5) Inflammatory — dermatomyositis, polymyositis, viral myositis. Complications: AKI (intrarenal injury from myoglobin), hyperkalemia (cardiac arrest risk), compartment syndrome (muscle swelling exceeds fascial envelope), DIC, hypocalcemia (then rebound hypercalcemia in recovery). Treatment: aggressive IV fluids (often 1–2 L/hr initial, then maintenance) to maintain high urine output; bicarbonate and mannitol controversial but commonly used; treat hyperkalemia urgently; monitor compartment pressures; dialysis if indicated. Most common lab pitfall: urine dipstick positive for blood without red cells on microscopy → myoglobinuria; RBCs would suggest true hematuria.