Rhabdomyolysis

Definition and epidemiology

Rhabdomyolysis is a clinical and biochemical syndrome resulting from skeletal muscle injury and necrosis, leading to the release of intracellular muscle constituents into the bloodstream. The hallmark is markedly elevated serum creatine kinase (CK), typically exceeding 1,000 U/L and often reaching 5,000–100,000 U/L or higher.

The incidence is approximately 26,000 cases annually in the United States, though mild cases are likely underreported. It accounts for approximately 7–10% of all cases of acute kidney injury in the U.S. Rhabdomyolysis can occur at any age but is more common in young adults, particularly males, due to higher rates of trauma, substance abuse, and intense physical exertion. The condition spans a spectrum from asymptomatic CK elevation to life-threatening complications including acute kidney injury (AKI), hyperkalemia, and disseminated intravascular coagulation (DIC).

Etiology and risk factors

Rhabdomyolysis has numerous causes, commonly grouped into traumatic and non-traumatic categories.

Traumatic causes

• Crush injury: prolonged compression of muscle (e.g., motor vehicle accidents, building collapse, prolonged immobilization)
• Intense exercise: particularly in untrained individuals, exertional heat stroke, military training
• Electrical injury: lightning strike, high-voltage electrical burns
• Burns and compartment syndrome

Non-traumatic causes

• Drugs and toxins: statins (especially with fibrates or CYP3A4 inhibitors), cocaine, amphetamines, MDMA (ecstasy), alcohol, heroin, antipsychotics causing neuroleptic malignant syndrome
• Infections: influenza A and B, HIV, Epstein-Barr virus, Coxsackie virus, Legionella, Streptococcus pyogenes, COVID-19
• Metabolic and electrolyte disorders: hypokalemia, hypophosphatemia, hypocalcemia, diabetic ketoacidosis, hypothyroidism, hyperthyroidism
• Genetic myopathies: McArdle disease (myophosphorylase deficiency), carnitine palmitoyltransferase II deficiency, malignant hyperthermia
• Prolonged immobilization: altered mental status from drug overdose, stroke, or psychiatric illness leading to prolonged recumbency
• Autoimmune myositis: dermatomyositis, polymyositis
• Serotonin syndrome: combination of serotonergic drugs

Risk factors include dehydration, extremes of temperature, genetic predisposition, concurrent nephrotoxic medications, baseline renal impairment, and metabolic acidosis.

Pathophysiology

Rhabdomyolysis results from disruption of skeletal muscle cell membrane integrity, leading to intracellular content leakage. The primary mechanism involves depletion of ATP, which impairs the sodium-potassium ATPase pump. This causes intracellular sodium and calcium accumulation, activating proteases and phospholipases that destroy the sarcolemma.

Muscle breakdown releases multiple substances into the circulation:

• Myoglobin: a 17-kDa heme protein filtered by the glomerulus. In acidic urine, myoglobin precipitates in renal tubules, causing direct tubular toxicity and obstruction. Myoglobin is also directly nephrotoxic through oxidative injury and lipid peroxidation.
• Creatine kinase (CK): peaks 24–36 hours after injury, with a half-life of 36 hours. CK MM isoenzyme predominates from skeletal muscle.
• Electrolytes: potassium, phosphate, and purines are released, causing hyperkalemia, hyperphosphatemia, hyperuricemia, and hypocalcemia (calcium precipitates with phosphate in damaged tissue).
• Organic acids: contribute to metabolic acidosis.

Acute kidney injury occurs in 10–50% of cases through three mechanisms: renal vasoconstriction (hypovolemia, myoglobin-induced vasoconstriction), direct tubular injury from myoglobin, and tubular obstruction by myoglobin casts. Acidic urine (pH < 6.5) and hypovolemia significantly increase the risk of AKI.

In the recovery phase, calcium is released from necrotic tissue, potentially causing hypercalcemia. Compartment syndrome may develop from muscle swelling, creating a self-perpetuating cycle of ischemia and further muscle necrosis.

Clinical features

The classic triad of rhabdomyolysis consists of muscle pain, weakness, and dark urine, though only 10% of patients present with all three features.

Symptoms

• Muscle pain (myalgia): present in 50–80% of cases, typically in large muscle groups (thighs, calves, lower back)
• Muscle weakness: difficulty standing from sitting, lifting objects
• Dark urine: tea-colored or cola-colored urine from myoglobinuria (appears when myoglobin > 100 mg/dL)
• Malaise, fever, nausea, vomiting: non-specific systemic symptoms
• Confusion: may result from electrolyte abnormalities or underlying cause

Signs

• Muscle tenderness and swelling: firm, tender muscles, especially in the calves and thighs
• Reduced urine output: oliguria or anuria suggests developing AKI
• Tachycardia and hypotension: from hypovolemia due to third-spacing of fluid into damaged muscle
• Cardiac arrhythmias: from hyperkalemia
• Compartment syndrome: tense, swollen compartment with severe pain, paresthesias, pallor, pulselessness (late finding)

Severe cases may progress to multiorgan failure with respiratory failure, DIC, and cardiovascular collapse. Asymptomatic presentations occur, particularly with mild CK elevations from statin use or subclinical viral myositis.

Diagnosis

Diagnosis is based on clinical suspicion and laboratory confirmation. The key diagnostic criterion is elevated serum CK, typically > 1,000 U/L (5 times the upper limit of normal), though levels > 5,000 U/L are more specific.

Laboratory findings

Serum studies:

• Creatine kinase (CK): markedly elevated, often 10,000–100,000 U/L or higher; peaks at 24–36 hours
• Myoglobin: elevated in serum (half-life 2–3 hours, so may be normal if presentation is delayed)
• Electrolytes: hyperkalemia, hyperphosphatemia, hypocalcemia (early), hyperuricemia
• Renal function: elevated BUN and creatinine suggest AKI; creatinine rises disproportionately to BUN
• Metabolic acidosis: elevated anion gap
• Liver enzymes: AST and ALT may be elevated (released from muscle)
• Lactate dehydrogenase (LDH): markedly elevated
• Calcium: hypocalcemia initially, hypercalcemia during recovery

Urine studies:

• Urinalysis: positive for blood on dipstick (detects heme) but few or no red blood cells on microscopy—this dissociation suggests myoglobinuria or hemoglobinuria
• Urine myoglobin: confirmatory but often not available rapidly; myoglobin is cleared quickly from urine
• Urine sediment: may show pigmented granular casts

Other studies:

• Electrocardiogram (ECG): to assess for hyperkalemia (peaked T waves, widened QRS)
• Compartment pressure measurement: if compartment syndrome suspected (pressure > 30 mmHg is abnormal)
• Toxicology screen: if substance abuse suspected
• Viral serologies, inflammatory markers (ESR, CRP): if infection or inflammatory myositis suspected
• Genetic testing: in recurrent cases or positive family history

Diagnostic criteria

Diagnosis requires CK > 1,000 U/L (or > 5 times upper limit of normal) in the appropriate clinical context. Myoglobinuria confirms the diagnosis but is not required.

Differential diagnosis

The differential diagnosis includes conditions that cause muscle pain, weakness, dark urine, or elevated CK:

• Acute kidney injury from other causes: pre-renal azotemia, acute tubular necrosis from other nephrotoxins, contrast-induced nephropathy. Distinguish by absence of markedly elevated CK and myoglobinuria.
• Hemoglobinuria: intravascular hemolysis (e.g., transfusion reaction, paroxysmal nocturnal hemoglobinuria, G6PD deficiency). Urine dipstick positive for blood with no RBCs on microscopy, but serum CK is normal and hemolysis markers (elevated LDH, low haptoglobin, elevated indirect bilirubin) are present.
• Inflammatory myopathies: polymyositis, dermatomyositis. Subacute onset, typically less dramatic CK elevation (usually < 10,000 U/L), positive autoantibodies (anti-Jo-1, anti-Mi-2), muscle biopsy shows inflammatory infiltrate.
• Compartment syndrome without rhabdomyolysis: severe pain, tense compartment, but CK may be normal or mildly elevated initially.
• Myocardial infarction: elevated CK-MB and troponin, but CK-MM (skeletal muscle) is not disproportionately elevated, and cardiac symptoms predominate.
• Statin-induced myopathy without rhabdomyolysis: muscle pain with normal or mildly elevated CK (< 1,000 U/L).
• Viral syndrome with myalgia: influenza, COVID-19. Mild CK elevation (typically < 1,000 U/L), no myoglobinuria.
• Neuroleptic malignant syndrome: fever, rigidity, altered mental status, autonomic instability, CK elevation. History of antipsychotic use.
• Serotonin syndrome: agitation, clonus, hyperreflexia, hyperthermia, recent increase in serotonergic drugs.
• Malignant hyperthermia: triggered by anesthetic agents (succinylcholine, volatile anesthetics), hyperthermia, rigidity, hypercarbia during surgery.

Management

The cornerstone of management is aggressive intravenous fluid resuscitation to prevent acute kidney injury. Early recognition and treatment significantly reduce morbidity and mortality.

Initial management

Fluid resuscitation:

• Isotonic saline (0.9% NaCl): start immediately, targeting high urine output to promote myoglobin clearance
• Goal: maintain intravascular volume, promote myoglobin clearance, prevent tubular obstruction
• Monitor for fluid overload, especially in patients with AKI or heart failure

Urine alkalinization (controversial):

• Historically advocated to reduce myoglobin precipitation in tubules (myoglobin more soluble at pH > 6.5)
• Method: add sodium bicarbonate to IV fluids to target urine pH > 6.5
• Current evidence does not strongly support routine use; adequate fluid resuscitation is more important
• May be considered in severe cases if urine pH remains < 6.0 despite fluids

Electrolyte management:

• Hyperkalemia: treat if severe (> 6.5 mEq/L) or ECG changes present—calcium gluconate (membrane stabilization), insulin with dextrose, sodium bicarbonate, loop diuretics, potassium-binding resins
• Hypocalcemia: do not treat unless symptomatic (tetany, seizures) as it may worsen tissue calcium deposition; calcium levels often normalize spontaneously
• Hyperphosphatemia: usually resolves with hydration; avoid phosphate binders unless severe

Discontinue causative agents: stop statins, nephrotoxic drugs, or other inciting medications.

Renal replacement therapy

Indications for dialysis:

• Severe hyperkalemia refractory to medical management
• Volume overload unresponsive to diuretics
• Severe metabolic acidosis (pH < 7.1)
• Uremic symptoms or complications (pericarditis, encephalopathy)
• Severe azotemia (BUN > 100 mg/dL)

Dialysis does not effectively remove myoglobin (too large, protein-bound) but treats complications of AKI.

Surgical management

• Fasciotomy: emergent surgical decompression if compartment syndrome present (compartment pressure > 30 mmHg, clinical signs of neurovascular compromise)
• Delay worsens outcomes; fasciotomy should be performed urgently

Additional supportive care

• Treat underlying cause (infection, hyperthermia, seizures)
• Pain management
• Monitor for complications: DIC (check PT, PTT, fibrinogen, D-dimer), arrhythmias (continuous cardiac monitoring)
• Avoid nephrotoxic agents (NSAIDs, aminoglycosides, contrast)

Disposition

• Mild cases (CK < 5,000 U/L, normal renal function, no complications): may be managed outpatient with oral hydration and close follow-up
• Moderate to severe cases: admit for IV fluid resuscitation and monitoring
• ICU admission: for severe cases (CK > 15,000–20,000 U/L, AKI, electrolyte abnormalities, multiorgan involvement)

Monitoring

• Serial CK, creatinine, electrolytes, urine output
• CK should decline by approximately 30–50% per day with treatment
• Persistent or rising CK suggests ongoing muscle injury

Complications and prognosis

Acute complications:

• Acute kidney injury (AKI): occurs in 10–50% of cases, most important complication. Risk factors include CK > 15,000 U/L, dehydration, acidic urine, pre-existing renal disease. Most cases recover renal function, but 5–10% may require long-term dialysis.
• Hyperkalemia: potentially fatal due to cardiac arrhythmias, especially when combined with acidosis and hypocalcemia.
• Hypocalcemia: early complication from calcium precipitation in damaged tissue; typically does not require treatment.
• Hypercalcemia: may occur during recovery (diuretic phase) as calcium is mobilized from necrotic tissue.
• Disseminated intravascular coagulation (DIC): occurs in severe cases, particularly with sepsis or massive muscle injury.
• Compartment syndrome: creates a vicious cycle of ischemia and further muscle necrosis if not decompressed.
• Metabolic acidosis: contributes to cardiac instability and worsens renal injury.
• Cardiac arrhythmias: from electrolyte disturbances (hyperkalemia, hypocalcemia) or direct myocardial involvement.
• Respiratory failure: from fluid overload, ARDS, or neuromuscular weakness.

Long-term complications:

• Chronic kidney disease: risk higher with severe or prolonged AKI, delayed treatment, or recurrent episodes.
• Muscle weakness and contractures: permanent muscle damage may occur in severe cases.
• Recurrent rhabdomyolysis: particularly in patients with underlying genetic disorders, metabolic myopathies, or continued risk factor exposure.

Prognosis:

Overall mortality ranges from 5% to 10% in hospitalized patients but can exceed 20% in those with severe AKI requiring dialysis or multiorgan failure. Mortality is primarily driven by the underlying cause, presence of AKI, complications, and delay in treatment.

With early recognition and aggressive fluid resuscitation, most patients recover fully. CK normalizes over 3–5 days, though may take up to 2 weeks in severe cases. Renal function typically improves within days to weeks, though some patients develop persistent CKD.

Predictors of poor outcome:

• Delayed presentation (> 12 hours after symptom onset)
• CK > 15,000–20,000 U/L
• Acute kidney injury requiring dialysis
• Sepsis or multiorgan failure
• Age > 65 years
• Pre-existing comorbidities (renal disease, heart failure)

Prevention in high-risk individuals:

• Gradual exercise training, adequate hydration during exertion
• Avoid combining statins with fibrates or strong CYP3A4 inhibitors (clarithromycin, erythromycin, grapefruit juice)
• Screen for CK and symptoms in patients on statins
• Genetic counseling for patients with recurrent episodes or positive family history

Practice questions

Frequently asked questions

Key drugs

Related conditions and differentials

Sources and further reading

StatPearls (NCBI Bookshelf)MedlinePlusWHO ICD-10: M62.8

Educational content for medical students, prepared by the WhiteCoat Pro editorial team with AI assistance; every page is reviewed by a second AI model for factual errors. It is not medical advice and does not replace the product label, local guidelines or a clinician.