Rhabdomyolysis is muscle damage caused by:
- Pressure or crush injury (e.g. prolonged unconsciousness)
- Ischaemic injury when blood supply is cut off
- Chemical injury (e.g. sometimes in those taking cholesterol-lowering statins)
It was first described in the Second World War (1939-45) in people trapped beneath bombed buildings. Huge numbers of cases may occur after earthquakes. The damaged muscle releases a number of things as perfusion is restored:
- Myoglobin – this small haem-containing protein is filtered at the glomerulus because of its small size, but is toxic to renal tubular cells. Its toxicity may be reduced by alkalinising the urine by giving sodium bicarbonate. Urine containing a lot of myoglobin is dark brown to black.
- Potassium – the levels may rise very rapidly and dangerously in ARF caused by rhabdomyolysis, requiring frequent and intensive dialysis.
- Phosphate – Levels rise very high, causing calcium phosphate to precipitate and leading to low calcium levels.
- Muscle enzymes – Creatine Phosphokinase (CPK) levels rise very high (to values of tens of thousands), a useful diagnostic test. LDH and some other enzymes will be elevated too; so will uric acid.
- Emergency treatment for hyperkalaemia. More about potassium
- Preventive treatment – fluid resuscitation to restore circulation and urine output. Include sodium bicarbonate in large quantities to alkalinise the urine.
- Dialysis if urine output not restored and biochemical changes dangerous
- Muscle compartment pressure may rise very high after muscle damage, cutting off blood supply. Compartment pressures can be measured, and operations to cut open the affected compartments can save further muscle damage, and may be needed urgently.
Recovery follows the standard pattern for ARF.