Rhabdomylysis
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I now have comprehensive information from Goldman-Cecil Medicine, Comprehensive Clinical Nephrology, and Tintinalli's Emergency Medicine. Let me compile a thorough, well-organized response.
Rhabdomyolysis
Definition
Rhabdomyolysis is an acute, potentially fatal syndrome reflecting the dissolution and disintegration of striated (skeletal) muscle, releasing intracellular contents into the systemic circulation. Key released substances include myoglobin, creatine kinase (CK), potassium, calcium, aldolase, lactate dehydrogenase, aspartate aminotransferase, and nucleic acids.
- Goldman-Cecil Medicine, p. 1159
Pathophysiology
The common terminal event across all causes involves:
- Na+/K+-ATPase pump disruption - impaired active transport leads to intracellular sodium accumulation
- Calcium influx - loss of membrane integrity allows extracellular Ca²+ to flood the cell
- Ca²+ activates phospholipase A2, proteases, and vasoactive molecules, generating free oxygen radicals -> muscle cell necrosis
Renal injury results from three mechanisms:
- Renal vasoconstriction reducing GFR
- Direct tubular toxicity - myoglobin (a heme-iron protein in the ferrous Fe²+ state) causes oxidative stress in proximal tubular cells
- Intratubular obstruction - myoglobin and uric acid precipitate in the distal tubule, especially in acidic urine and with volume depletion
AKI risk is lower when CK is <20,000 U/L, but rhabdomyolysis can cause AKI at levels as low as 5,000 U/L when compounded by sepsis, volume contraction, or acidosis.
- Comprehensive Clinical Nephrology 7e, p. 991
Causes
Inherited
| Category | Example |
|---|---|
| Glycolytic/glycogenolytic | McArdle disease (myophosphorylase deficiency) |
| Fatty acid oxidation | Carnitine palmitoyltransferase II (CPT-II) deficiency |
| Mitochondrial respiratory chain | Succinate dehydrogenase deficiency |
| Krebs cycle | Aconitase deficiency |
| Malignant hyperthermia susceptibility | RYR1 mutations, Duchenne/Becker dystrophies |
Acquired (most common)
| Category | Examples |
|---|---|
| Trauma/Crush | Crush injury, prolonged immobilization, electrical/lightning injury |
| Exertion | Strenuous exercise, CrossFit, spinning, seizures, CPR, status epilepticus |
| Drugs of abuse | Cocaine (20% of overdoses), heroin, alcohol, amphetamines, PCP, ecstasy |
| Medications | Statins, antipsychotics, SSRIs, colchicine, corticosteroids, propofol, barbiturates |
| Infections | Influenza A/B, EBV, HIV, HSV, CMV, COVID-19, Legionella, Group A Strep |
| Temperature extremes | Heatstroke, neuroleptic malignant syndrome (NMS), malignant hyperthermia, hypothermia |
| Metabolic/electrolyte | Hypokalemia, hypophosphatemia, hypocalcemia, DKA, nonketotic hyperosmolar states |
| Ischemia | Arterial occlusion, compartment syndrome, sickle cell disease, DIC |
| Inflammatory | Polymyositis, dermatomyositis |
Multiple causes are present in >50% of patients. In adults, drugs/alcohol are the most common cause. In children, viral myositis and trauma predominate.
- Goldman-Cecil Medicine, Table 99-1 | Tintinalli's Emergency Medicine, Table 89-1
Epidemiology
- ~26,000 hospitalized cases/year in the United States
- AKI develops in 13-67% of cases
- Rhabdomyolysis-associated AKI accounts for 5-10% of all AKI in the US
- AKI from rhabdomyolysis is independently associated with longer hospitalization and higher mortality
- Goldman-Cecil Medicine, p. 1160
Clinical Features
| Feature | Details |
|---|---|
| Myalgias/weakness | Present in only ~50% of cases - absence does not exclude diagnosis |
| Dark/cola-colored urine | Classic finding - due to myoglobinuria |
| Malaise, low-grade fever | Common nonspecific symptoms |
| Swelling/tenderness | Localized or diffuse depending on cause |
| Nausea, vomiting, abdominal pain | Seen in severe cases |
| Tachycardia | Common |
| Mental status changes | From uremic encephalopathy in severe AKI |
| Oliguria/anuria | Signal of developing AKI |
The classic triad is myalgia + weakness + dark urine, but the full triad is present in a minority of patients.
Complications
| Complication | Mechanism |
|---|---|
| Acute kidney injury | Myoglobin tubular toxicity + vasoconstriction + obstruction |
| Hyperkalemia | K+ released from necrotic muscle cells; can be life-threatening |
| Hypocalcemia (early) | Ca²+ sequestration in damaged muscle |
| Hypercalcemia (late) | Mobilization of calcium from necrotic muscle during recovery |
| Metabolic acidosis | Organic acid release + lactic acidosis |
| DIC | Release of thromboplastin from necrotic muscle |
| Compartment syndrome | Muscle edema increases compartment pressure |
| Arrhythmias | Hyperkalemia + hypocalcemia + acidosis |
| Cardiac arrest | Electrolyte-driven fatal arrhythmia |
Diagnosis
Most sensitive test: Serum CK (elevated >5x upper limit of normal; often >10,000-100,000 U/L in significant rhabdomyolysis)
| Test | Finding |
|---|---|
| Serum CK | Markedly elevated - most reliable indicator of muscle injury |
| Urinalysis | "Blood" positive on dipstick (detects myoglobin), but no RBCs on microscopy |
| Urine microscopy | Pigmented granular ("muddy brown") casts |
| Urine myoglobin | Confirms myoglobinuria |
| BMP | Hyperkalemia, elevated creatinine/BUN, metabolic acidosis |
| Phosphorus | Elevated (released from cells) |
| Calcium | Low early, may rise late |
| LDH, AST | Elevated (nonspecific) |
| CBC | May show leukocytosis |
| Coagulation studies | Screen for DIC |
Key diagnostic clue: dipstick positive for blood + no RBCs on microscopy + elevated CK = rhabdomyolysis until proven otherwise.
- Comprehensive Clinical Nephrology 7e, p. 991
Treatment
1. Aggressive IV Fluid Resuscitation (cornerstone of therapy)
- Begin isotonic saline (0.9% NaCl) immediately - goal is to increase urine output to 200-300 mL/hour (or 3 mL/kg/hour)
- Prevents tubular obstruction, dilutes myoglobin, and restores renal perfusion
- Typical initial rates: 1-1.5 L/hour in adults until urine output target is met
- May require large volumes (10+ liters in first 24h in severe cases)
2. Urinary Alkalinization (controversial, may be beneficial)
- IV sodium bicarbonate added to IV fluid (target urine pH >6.5)
- Alkaline urine reduces myoglobin precipitation in tubules
- Benefit remains debated; avoid if metabolic alkalosis or hypocalcemia worsens
3. Electrolyte Management
- Hyperkalemia - treat aggressively (calcium gluconate for membrane stabilization, insulin/glucose, bicarbonate, kayexalate, dialysis if refractory)
- Hypocalcemia - treat only if symptomatic or severe; do NOT correct asymptomatic hypocalcemia (late hypercalcemia can result)
- Monitor phosphorus closely
4. Treat the Underlying Cause
- Discontinue offending drugs (statins, antipsychotics)
- Treat infections, metabolic disorders, hyperthermia
- Fasciotomy for compartment syndrome
5. Dialysis
- Indicated for refractory AKI, severe hyperkalemia not responding to medical treatment, fluid overload, or severe acidosis
6. Monitoring
- Serial CK, BMP, urine output every 4-6 hours initially
- CK typically peaks at 24-72 hours, then declines if the trigger is removed
Statin-Specific Notes
- Up to 10% of statin users develop myalgias; rhabdomyolysis rates are 0-2.2 cases/1000 person-years
- Cerivastatin had the highest rates (withdrawn from market)
- Risk greatly increased with polypharmacy: cyclosporine, macrolide antibiotics, azole antifungals, fibrates (especially gemfibrozil)
- Statins can also cause an autoimmune anti-HMG-CoA reductase antibody myopathy with profound CK elevation - this does NOT resolve with statin discontinuation and requires immunosuppression
- Goldman-Cecil Medicine, p. 1160
Exertional Rhabdomyolysis
Risk factors specific to exercise-related cases:
- High-intensity eccentric/resistance training (more muscle breakdown than concentric/aerobic)
- Poor conditioning, sudden increase in exercise intensity
- Male sex, dehydration, heat and humidity
- Restrictive clothing
- Use of dietary supplements with stimulant combinations
- Sickle cell trait (increased susceptibility)
Recent Evidence (PubMed, 2024-2026)
- A 2025 systematic review and meta-analysis specifically on pediatric rhabdomyolysis (PMID: 41146051) examined etiologies, management, and outcomes in children - confirming viral myositis and trauma as dominant causes in the pediatric population, with generally more benign outcomes than adults.
- A 2024 systematic review (PMID: 38987799) examined the statin-quinolone drug-drug interaction and associated rhabdomyolysis risk - concurrent use increases myotoxicity risk.
Key Takeaway: Rhabdomyolysis is a clinical diagnosis supported by markedly elevated CK and urinary myoglobin. The cornerstone of management is early and aggressive IV hydration to prevent and treat AKI. Always search for the underlying cause, monitor electrolytes closely, and watch for complications including hyperkalemia, which can be immediately life-threatening.
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