How do you diagnose rhabdomyolysis?

Diagnosing Rhabdomyolysis

The diagnosis of rhabdomyolysis requires measurement of serum creatine kinase (CK), creatinine, and urinalysis for myoglobinuria. 1 CK is the biochemical gold standard for diagnosis, with levels typically elevated at least 5-10 times the upper limit of normal.

Diagnostic Approach

Laboratory Assessment

1. Serum Creatine Kinase (CK)

   • Primary diagnostic marker
   • Diagnostic threshold: At least 5-10 times the upper limit of normal 2
   • Severe cases may show levels >15,000-100,000 IU/L 2
   • CK typically peaks within 24-72 hours and decreases gradually over 3-5 days

2. Urinalysis

   • Check for myoglobinuria (dipstick positive for blood without RBCs on microscopy) 1
   • Urine appears red to brown/tea-colored in classic cases

3. Additional Laboratory Tests

   • Serum myoglobin (rises and falls more rapidly than CK)
   • Comprehensive metabolic panel:
     • Creatinine and BUN (to assess kidney function)
     • Electrolytes (particularly potassium, calcium, phosphate)
     • Liver function tests (may be elevated)
   • Complete blood count
   • Coagulation studies if DIC suspected

Clinical Assessment

• Muscle pain, tenderness, swelling (classic triad with myoglobinuria seen in <10% of cases) 2
• Muscle weakness
• Signs of volume depletion
• Assess for compartment syndrome in traumatic cases

Identifying Underlying Causes

Determine potential causes through targeted history:

• Trauma or crush injury
• Extreme physical exertion
• Prolonged immobilization
• Medications (statins, antipsychotics)
• Substance use (alcohol, illicit drugs)
• Recent infections
• Seizures
• Metabolic disorders
• Exposure to extreme temperatures

Assessing Complications

1. Acute Kidney Injury

   • Most serious complication, occurring in 13-50% of cases 3
   • Higher risk when CK >16,000 IU/L 2
   • Monitor urine output, creatinine, and BUN

2. Electrolyte Abnormalities

   • Hyperkalemia (can be life-threatening)
   • Hypocalcemia (early)
   • Hyperphosphatemia
   • Hyperuricemia

3. Other Complications

   • Compartment syndrome
   • Disseminated intravascular coagulation (DIC)
   • Metabolic acidosis

Management Considerations

If rhabdomyolysis is suspected:

• For severe symptoms (CK >5 times normal with muscle pain, weakness, or dark urine):

  • Immediately discontinue any potential causative medications 1
  • Initiate aggressive IV fluid resuscitation
  • Target urine output of 300 mL/hour 4
  • Monitor electrolytes frequently
  • Consider ICU admission for severe cases

• For mild to moderate symptoms:

  • Evaluate for other conditions that might increase risk 1
  • Discontinue potential causative medications
  • Provide adequate hydration

Pitfalls to Avoid

1. Delayed Recognition

   • Rhabdomyolysis can present with nonspecific symptoms
   • Don't wait for the classic triad (present in <10% of cases) 2
   • Consider in high-risk scenarios even without obvious symptoms

2. Inadequate Fluid Resuscitation

   • Aggressive hydration is critical to prevent kidney injury
   • Underestimating fluid needs can lead to acute kidney injury

3. Missing Compartment Syndrome

   • Assess for signs of compartment syndrome in traumatic cases
   • Pain out of proportion to exam, paresthesias, pallor, pulselessness

4. Overlooking Severe Hyperkalemia

   • Can cause life-threatening cardiac arrhythmias
   • Obtain ECG and monitor potassium levels closely

5. Failure to Identify Underlying Cause

   • Recurrent episodes warrant investigation for genetic disorders 2
   • Addressing the underlying cause is essential for management

Remember that early recognition and aggressive treatment are key to preventing complications of rhabdomyolysis, particularly acute kidney injury which significantly increases mortality risk.