What are the signs of rhabdomyolysis?

Signs of Rhabdomyolysis

Rhabdomyolysis is characterized by elevated serum creatine kinase (CK) levels at least 10 times the upper limit of normal, with the classic triad of myalgia, muscle weakness, and pigmenturia present in less than 10% of cases. 1, 2

Clinical Presentation

Common Signs and Symptoms

• Muscle symptoms:

  • Muscle pain (myalgia)
  • Muscle weakness
  • Muscle tenderness
  • Stiffness
  • Cramping
  • Fatigue 3, 1

• Urinary changes:

  • Dark, tea-colored or cola-colored urine (due to myoglobinuria)
  • Decreased urine output in severe cases 1, 4

• Systemic symptoms:

  • Fever
  • Malaise
  • Nausea and vomiting
  • Confusion (in severe cases) 1

Laboratory Findings

• Definitive diagnostic markers:

  • Elevated serum CK (at least 10× upper limit of normal)
  • CK levels may peak 24-72 hours after muscle injury
  • Myoglobinuria (myoglobin in urine) 1, 4, 2

• Additional laboratory abnormalities:

  • Hyperkalemia (elevated potassium)
  • Hypocalcemia (decreased calcium)
  • Hyperphosphatemia (elevated phosphate)
  • Elevated creatinine and blood urea nitrogen (BUN)
  • Metabolic acidosis 1, 5

Complications to Monitor

Acute Kidney Injury

• Most significant complication of rhabdomyolysis
• Signs include:
  • Decreased urine output
  • Rising creatinine levels
  • Fluid overload 1, 4

Compartment Syndrome

• May develop as early or late finding
• Key signs:
  • Pain disproportionate to injury
  • Tension in affected compartment
  • Paresthesia (abnormal sensations)
  • Paresis (weakness)
  • Pallor and pulselessness (late findings) 1

Electrolyte Disturbances

• Hyperkalemia can lead to cardiac arrhythmias
• ECG changes (peaked T waves, widened QRS, prolonged PR interval)
• Symptomatic hypocalcemia may cause tetany, seizures 1, 6

Diagnostic Approach

1. Laboratory evaluation:

   • Serum CK levels (diagnostic threshold: ≥10× upper limit of normal)
   • Urinalysis for myoglobinuria
   • Plasma myoglobin (confirms muscle breakdown but has shorter half-life of 2-3 hours)
   • Serum electrolytes, BUN, and creatinine
   • ECG to assess for cardiac complications 1, 4, 2

2. Differential diagnosis considerations:

   • Myositis: both have elevated CK, but inflammatory markers typically higher in myositis
   • Autoantibody testing may be needed to differentiate 1

Clinical Pitfalls and Caveats

• The classic triad of myalgia, weakness, and pigmenturia is present in less than 10% of cases, making diagnosis challenging 1, 2
• CK levels can be extremely high (up to 100,000 IU/L) in severe cases 2
• Risk of acute kidney injury increases significantly when CK levels exceed 16,000 IU/L 2
• Plasma myoglobin has a shorter half-life than CK and may return to normal while CK remains elevated 1
• Recurrent episodes of rhabdomyolysis should prompt investigation for underlying genetic disorders 1, 7
• In statin users with unexplained severe muscle symptoms, promptly discontinue the medication and evaluate for rhabdomyolysis 3

High-Risk Scenarios

• Statin use, especially at higher doses or when combined with other medications like fibrates (particularly gemfibrozil) 3, 1
• Trauma or crush injuries
• Prolonged immobilization
• Seizures
• Severe infections
• Drug toxicity
• Excessive exercise, especially in untrained individuals 1, 4, 6

Early recognition of rhabdomyolysis is crucial for preventing complications, particularly acute kidney injury, which significantly increases mortality risk.