A condition where skeletal muscle tissue breaks down and releases breakdown products into the blood, usually triggered by an event that causes the muscle to break down e.g. extreme underuse or overuse or a traumatic injury

Aetiology

• Anything that causes significant damage to muscle cells can cause rhabdomyolysis:
  • Prolonged immobility, particularly frail patients that fall and spend time on the floor before being found
  • Extremely rigorous exercise beyond the person’s fitness level (e.g. ultramaraton, triathalon, crossfit competition)
  • Crush injuries
  • Seizures

Pathophysiology

• The muscle cells (myocytes) undergo apoptosis which results in muscle cells releasing:
  • Myoglobin (causing myoglobinurea)
  • Potassium - the most immediately dangerous breakdown product as hyperkalaemia can cause arrhymias
  • Phosphate
  • Creatine kinase
• These breakdown products are filtered by the kidney and cause injury to the kidney
  • Myoglobin in particular is toxic to the kidney in high concentrations - results in acute kidney injury

Clinical features

• Muscle aches and pain
• Oedema
• Fatigue
• Confusion (particularly in elderly frail patients)
• Red-brown urine

Investigations

• Bloods:
  • Creatinine kinase ↑↑
  • U+Es for AKI and hyperkalaemia
• Urinalysis: red-brown colour due to myoglobinurea, will be positive for blood
• ECG: important in assessing the heart’s response to hyperkalaemia

Management

• IV fluids are the mainstay of treatment
  • Normal saline should be used
  • Hartmann’s may be used in this situation but is less appropriate than normal saline due to the potassium content which can worsen AKI