How should I evaluate and treat a patient with suspected rhabdomyolysis?

Evaluation and Treatment of Suspected Rhabdomyolysis

Immediately initiate aggressive intravenous fluid resuscitation with 0.9% normal saline at 1 liter per hour while simultaneously obtaining creatine kinase (CK), comprehensive metabolic panel, and urinalysis—this is the single most critical intervention to prevent acute kidney injury. 1, 2

Diagnostic Workup

Essential Initial Laboratory Tests

Obtain the following tests immediately upon suspicion:

• Creatine kinase (CK): Diagnostic threshold is CK ≥5-10 times the upper limit of normal (typically >1,000 U/L, with severe cases >50,000 U/L) 1, 3
• Comprehensive metabolic panel: Including creatinine, BUN, electrolytes (especially potassium), glucose, calcium, and phosphorus 1
• Urinalysis: Look for myoglobinuria—brown or dark urine that is positive for blood without red blood cells present 1
• Complete blood count with differential: To evaluate for infection or systemic processes 1
• Arterial blood gas: To assess for metabolic acidosis, which commonly occurs in severe cases 4, 1
• ECG: Perform immediately to assess for arrhythmias related to hyperkalemia 1

Additional Muscle Enzymes

Measure LDH, AST (SGOT), ALT (SGPT), and aldolase, as these are commonly elevated and support the diagnosis 4, 1

Cardiac Assessment

Check cardiac troponin in patients with severe rhabdomyolysis to rule out cardiac involvement—use total CK, not CK-MB, as CK-MB lacks sensitivity and specificity for rhabdomyolysis assessment 4, 1

Etiology-Specific Testing

Based on clinical presentation, consider:

• Medication review: Document all prescription medications (especially statins), over-the-counter drugs, herbal supplements, and performance-enhancing products 4
• Recreational drug screen: Ask specifically about cocaine, methamphetamine, ecstasy (MDMA), ketamine, and heroin 4
• Thyroid function tests: Hypothyroidism predisposes to statin-induced rhabdomyolysis 4, 1
• Autoimmune markers: If autoimmune myositis suspected, check ANA, anti-CCP, rheumatoid factor, and myositis-specific antibodies 1
• Genetic testing: For recurrent rhabdomyolysis, consider RYR1 and CACNA1S gene sequencing (malignant hyperthermia susceptibility) or CPT2, PYGM, ACADM, AMPD1, VLCAD gene testing (metabolic myopathies) 4

Severity Stratification

Classify severity to guide fluid resuscitation volume:

• Mild: CK <15,000 IU/L, normal renal function, no significant electrolyte abnormalities 1
• Moderate: CK 15,000-50,000 IU/L, mild renal dysfunction—requires 3-6L fluid per day 4, 1
• Severe: CK >50,000 IU/L, acute kidney injury—requires >6L fluid per day 4, 1

Fluid Resuscitation Protocol

Initial Resuscitation

Start 0.9% normal saline at 1,000 mL/hour immediately—early initiation is critical, as delayed treatment is associated with higher risk of acute kidney injury 4, 2

• If resuscitation extends beyond 2 hours, reduce infusion rate by at least 50% to avoid volume overload 2
• Target urine output of ≥300 mL/hour (approximately 3-5 mL/kg/hour for a 70 kg patient) 2, 3, 5
• Insert bladder catheter to monitor hourly urine output unless urethral injury is suspected 2

Fluid Type Selection

• Use isotonic saline (0.9% NaCl) as the primary crystalloid 2
• Avoid potassium-containing fluids (Lactated Ringer's, Hartmann's solution, Plasmalyte A)—potassium levels can increase markedly after reperfusion even with intact renal function 2
• Avoid starch-based colloids—associated with higher rates of AKI and bleeding 2

Duration of Fluid Therapy

Continue IV fluids until CK <1,000 U/L and renal function is stable 1, 3

Critical Electrolyte Management

Hyperkalemia

Monitor potassium every 6-12 hours in severe cases—hyperkalemia can precipitate life-threatening cardiac arrhythmias and cardiac arrest 4, 1

If life-threatening hyperkalemia develops despite medical management, initiate renal replacement therapy 4

Hypocalcemia and Hyperphosphatemia

Monitor calcium and phosphorus levels closely—these are common complications 1

Do not routinely correct hypocalcemia unless symptomatic, as calcium can precipitate in damaged muscle tissue 4

Interventions NOT Recommended

Urinary Alkalinization with Bicarbonate

Do not use routine bicarbonate administration for urinary alkalinization—current evidence shows no benefit over aggressive saline resuscitation alone for preventing pigment nephropathy 2

• Large bicarbonate doses can worsen hypocalcemia by decreasing ionized calcium 2
• Reserve bicarbonate only for life-threatening hyperkalemia or severe metabolic acidosis, following standard critical care dosing 2

Mannitol

Do not routinely use mannitol—studies show little additional benefit compared to crystalloid resuscitation alone, and it is potentially nephrotoxic 2

Mannitol may only benefit patients with CK >30,000 U/L, though this benefit remains undefined, and it is contraindicated in oligoanuria 2

Loop Diuretics

Diuretics should only be considered after adequate volume expansion for management of volume overload, not as primary treatment 2, 5

Monitoring During Treatment

Serial Laboratory Monitoring

• CK levels: Trend daily until declining 1
• Electrolytes (especially potassium): Every 6-12 hours in severe cases 1
• Renal function (creatinine, BUN): Daily until stable 1
• Urine output: Hourly monitoring 1

Important timing consideration: CK levels peak 24-120 hours after the inciting event, so initial levels may not represent the peak 4

Medication Management

Immediately discontinue any causative agents, particularly:

• Statins (most common drug cause, incidence 1.6 per 100,000 patient-years) 4
• Red yeast rice containing lovastatin 4
• Creatine monohydrate 4
• Wormwood oil, licorice, Hydroxycut 4

Avoid succinylcholine in perioperative patients, as it can exacerbate rhabdomyolysis 4

Pain Management

• First-line: Acetaminophen 500-1,000 mg (maximum 4-6 grams daily)—avoids nephrotoxic effects 4
• Avoid all NSAIDs (ibuprofen, ketoprofen, diclofenac, naproxen, mefenamic acid) due to renal toxicity 4
• For severe pain: Oral morphine 20-40 mg for opioid-naive patients; if GFR <30 mL/min, use fentanyl or buprenorphine 4

Compartment Syndrome Surveillance

Monitor for early signs: pain, tension, paresthesia, and paresis 4

Consider fasciotomy when:

• Compartment pressure exceeds 30 mmHg, OR
• Differential pressure (diastolic BP – compartment pressure) is <30 mmHg 4

Late signs (pulselessness, pallor) indicate irreversible damage 4

Renal Replacement Therapy Indications

Initiate dialysis for:

• Life-threatening hyperkalemia unresponsive to medical management 4
• Volume overload despite diuretic therapy 4
• Uremic symptoms (nausea, vomiting, pericarditis, encephalopathy) 4

Intermittent hemodialysis is the preferred modality—provides rapid potassium clearance 2

Special Clinical Scenarios

Altered Mental Status

Evaluate whether AMS is:

• A precipitating cause (seizures, prolonged immobilization, drug intoxication)
• A consequence (electrolyte disturbances, uremia from AKI)
• An unrelated complicating condition (neuroleptic malignant syndrome, serotonin syndrome) 4

Corticosteroid Use

Do not discontinue corticosteroids in patients with severe rhabdomyolysis—they may act therapeutically rather than as a causative agent 4

If immune-mediated myositis is confirmed, initiate high-dose corticosteroids (1-2 mg/kg/day prednisone equivalent) 4

Trauma-Related Cases

Impact trauma from falls can drastically increase CK without true muscle breakdown—CK elevation from simple contusion may not carry the same AKI risk 4

However, if CK is trending upward (doubling), assume true muscle breakdown until proven otherwise 4

Common Pitfalls to Avoid

• Delayed fluid resuscitation: Associated with significantly higher AKI risk 4, 2
• Using potassium-containing fluids: Can exacerbate life-threatening hyperkalemia 2
• Routine bicarbonate use: No proven benefit and can worsen hypocalcemia 2
• Premature discontinuation of fluids: Continue until CK <1,000 U/L 1, 3
• Failure to monitor for compartment syndrome: Can develop as early or late complication 4, 3
• Using CK-MB instead of total CK: CK-MB lacks sensitivity for rhabdomyolysis diagnosis 4