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Rhabdomyolysis

BASICS

  • Definition: Breakdown of muscle fibers with release of intracellular contents (myoglobin, CK, potassium) into bloodstream; commonly presents with muscle pain, weakness, and reddish-brown urine.
  • Classic Triad: Muscle pain, weakness, tea-colored urine (present in minority). Up to 50% are asymptomatic.

EPIDEMIOLOGY

  • More common in males, <10 years, >60 years, BMI >40
  • ~25,000 cases/year in US
  • Statin-induced rhabdomyolysis is rare (<0.5%)

ETIOLOGY & PATHOPHYSIOLOGY

Most common: Direct muscle trauma (crush injury, prolonged compression, surgery, burns, electric shock)

Other causes: - Exertion: Marathon, seizures, NMS, malignant hyperthermia - Drugs/toxins: Statins, fibrates, antipsychotics, alcohol, cocaine, heroin, amphetamines, colchicine, corticosteroids, antimalarials, zidovudine, carbon monoxide, snake/scorpion bites - Ischemia: Thrombosis, compartment syndrome, sickle cell, tourniquet - Infections: Viral (influenza, HIV, coxsackie), bacterial (Strep, Staph, Salmonella, Legionella), malaria - Temperature extremes: Hypo/hyperthermia - Metabolic/endocrine: DKA, hypo/hyperthyroidism, electrolyte disturbances (hyponatremia, hypokalemia, etc.) - Genetic/metabolic: Dystrophies, disorders of glycogen or lipid metabolism, mitochondrial diseases

PREVENTION

  • Avoid excessive exertion, maintain hydration
  • Avoid precipitating drugs/metabolic derangements

DIAGNOSIS

History

  • Trauma, immobilization, exertion, drug/toxin exposure, infection, recent seizure or surgery
  • Symptoms: malaise, muscle pain/cramps, weakness, fatigue, nausea, vomiting, fever, dark urine

Physical Exam

  • Muscle tenderness (proximal > distal), swelling, weakness, possible compartment syndrome
  • Tea-colored urine (myoglobinuria)
  • Vital sign abnormalities, possible signs of systemic illness

Differential Diagnosis

  • Other causes of dark urine (hemoglobinuria, nephritic syndromes, porphyria)
  • Inflammatory myopathies, infection, genetic muscle disorders

Diagnostic Tests

  • Serum CK: >5× upper limit normal (>1,000 U/L); often >5,000 U/L in severe cases; peaks 24–72h, normal in 3–5d
  • Urinalysis: Positive for blood (heme) without RBCs on microscopy (suggests myoglobinuria)
  • Myoglobin: Peaks early; may normalize before CK
  • Electrolytes: Hyperkalemia, hyperphosphatemia, initial hypocalcemia (late hypercalcemia during recovery), hyperuricemia, transaminitis (ALT, AST)
  • Renal function: Increased BUN/creatinine indicates ARF
  • Coagulation: Possible DIC in severe cases (↑PT/PTT, ↓platelets/fibrinogen)
  • ECG: For hyperkalemia (peaked T-waves)
  • Imaging: US for muscle swelling/edema; compartment pressure if suspected

TREATMENT

General Measures

  • Immediate cessation of causative agents (statins, drugs)
  • Aggressive IV fluid hydration (NS, 5% glucose; alternate to avoid volume overload)
  • Target urine output: 200–300 mL/hr (infusion: ~500 mL/hr)
  • Treat underlying cause (trauma, infection, etc.)
  • Monitor and correct electrolyte disturbances (esp. potassium)
  • Avoid unnecessary diuretics (unless volume overload or persistent oliguria)

Medications/Adjuncts

  • First line: IV fluids (mainstay)
  • Second line:
  • Alkalinization (bicarb) to maintain urine pH >6.5 (controversial)
  • Mannitol IV if inadequate urine output (controversial)
  • Furosemide if needed, not in anuric patients
  • Hyperkalemia:
  • Calcium gluconate (cardiac protection)
  • Sodium bicarbonate, insulin + glucose, albuterol, Kayexalate as needed
  • Dialysis if refractory/symptomatic hyperkalemia, persistent oliguria/anuria, volume overload, severe acidosis

Additional Therapies

  • Surgical consult for compartment syndrome (fasciotomy)
  • Dialysis for ARF as indicated
  • Treat DIC, hepatic dysfunction supportively

ADMISSION & INPATIENT CARE

  • Admit for significant CK elevation, renal impairment, or systemic symptoms
  • Monitor CK trend, renal function, electrolytes
  • Discharge only when CK is trending down and renal function is stable

FOLLOW-UP

  • Recheck CK, renal function, electrolytes in a few days post-discharge
  • For metabolic/genetic myopathies: specialist follow-up

DIET

  • In renal failure: restrict protein, potassium, and fluids as appropriate

PROGNOSIS

  • Good with early recognition, hydration, and supportive care
  • Complications: acute renal failure (most serious), hyperkalemia, DIC, hepatic dysfunction, compartment syndrome, death if untreated

ICD-10 CODES

  • M62.82: Rhabdomyolysis
  • T79.6: Traumatic ischemia of muscle
  • T79.6xxS: Traumatic ischemia of muscle, sequela

CLINICAL PEARLS

  • CK elevation is diagnostic hallmark
  • Aggressive fluid administration is the cornerstone of management
  • Monitor for AKI, electrolyte disturbances, hepatic injury, compartment syndrome, DIC
  • Initial serum creatinine is a key mortality predictor