What is the initial workup and management for a patient suspected of having rhabdomyolysis (muscle breakdown disease)?

Initial Workup and Management of Rhabdomyolysis

The initial workup for suspected rhabdomyolysis should include serum creatine kinase (CK) measurement (diagnostic threshold ≥10× upper limit of normal), urinalysis for myoglobinuria, and aggressive hydration with isotonic saline targeting urine output >300 mL/hour to prevent acute kidney injury. 1

Diagnostic Workup

Laboratory Tests

• Serum CK: Primary diagnostic marker
  • Diagnostic threshold: ≥10× upper limit of normal
  • Peak levels occur 24-72 hours after muscle injury
  • Serial monitoring recommended every 6-12 hours in acute phase 1
• Plasma myoglobin: Confirms muscle breakdown
  • Rises earlier than CK but has shorter half-life (2-3 hours) 1
• Urinalysis:
  • Check for myoglobinuria (tea/cola-colored urine)
  • Positive for blood on dipstick but negative for RBCs on microscopy 1
• Electrolytes:
  • Potassium (hyperkalemia is common)
  • Calcium (hypocalcemia may occur)
  • Phosphate (hyperphosphatemia)
  • Creatinine and BUN (to assess renal function) 1

Additional Tests

• Electrocardiogram: To assess for cardiac complications and effects of electrolyte abnormalities 2
• Chest radiograph: If respiratory symptoms are present 2
• Arterial blood gases: For patients with SaO₂ <92% or features of severe illness 2

Management

Immediate Interventions

1. Aggressive fluid resuscitation:

   • Isotonic saline (0.9% NaCl) is the initial fluid of choice
   • Avoid potassium-containing fluids (e.g., Lactated Ringer's)
   • Target urine output >300 mL/hour 1, 3

2. Electrolyte management:

   • Urgent correction of hyperkalemia if present
   • Address symptomatic hypocalcemia
   • Monitor and correct electrolyte abnormalities 1

3. Discontinue causative agents:

   • Stop medications that may cause or exacerbate rhabdomyolysis (e.g., statins)
   • Avoid all nephrotoxic medications (NSAIDs, ACE inhibitors/ARBs, certain antibiotics) 1

Monitoring

• Serial CK measurements every 6-12 hours until declining 1
• Frequent monitoring of electrolytes, especially potassium
• Continuous assessment of renal function
• Monitor for signs of compartment syndrome (pain, tension, paresthesia, paresis in affected limbs) 1

Management of Complications

Acute Kidney Injury

• Nephrology consultation for all cases with acute kidney injury
• Consider renal replacement therapy for:
  • Severe hyperkalemia
  • Acidosis
  • Volume overload
  • Uremic symptoms 1

Compartment Syndrome

• Remove tight dressings and avoid limb elevation if suspected
• Urgent surgical consultation for fasciotomy if confirmed
• Fasciotomy indicated for:
  • Hypotensive patients with intracompartment pressures ≥20 mmHg
  • Uncooperative/unconscious patients with pressures ≥30 mmHg
  • Normotensive patients with positive clinical findings and pressures ≥30 mmHg 1

Special Considerations

Genetic Factors

• Consider genetic causes in cases of recurrent rhabdomyolysis, exercise intolerance, or positive family history
• Obtain detailed three-generation family history to identify possible inherited disease patterns 1

Differential Diagnosis

• Myositis: Both have elevated CK, but inflammatory markers typically higher in myositis 1
• Other causes of acute kidney injury
• Other causes of pigmenturia

Common Pitfalls and Caveats

1. Relying on classic triad: The classic triad of myalgia, muscle weakness, and pigmenturia is present in less than 10% of cases 1, 4

2. Delayed treatment: Benefits of fasciotomy decrease significantly if delayed beyond 8 hours 1

3. Inadequate fluid resuscitation: Insufficient volume expansion increases risk of acute kidney injury 3

4. Overreliance on bicarbonate and mannitol: Evidence does not strongly support routine use of bicarbonate or mannitol in all cases of rhabdomyolysis 3, 5

5. Missing underlying causes: Failure to identify and address the underlying cause can lead to recurrence or ongoing muscle damage 1

The most recent evidence strongly supports aggressive fluid resuscitation with isotonic saline as the cornerstone of rhabdomyolysis management to prevent acute kidney injury, which occurs in up to 57% of untreated cases 1, 3.