Expansion
Muscle injury from any cause, with rhabdomyolysis at the extreme
Expansion
Causes
- Physiological: exercise, particularly unaccustomed or eccentric, and higher baselines in men, in people of African ancestry and in the muscular
- Trauma: crush injury, surgery, burns, prolonged immobility and a long lie, intramuscular injection, seizures, electrocution
- Drugs and toxins: statins, fibrates, alcohol, cocaine, amphetamines, heroin, neuroleptic malignant syndrome, malignant hyperthermia
- Muscle disease: polymyositis and dermatomyositis, muscular dystrophy, metabolic myopathy, hypothyroidism
- Ischaemia: limb ischaemia, compartment syndrome
- Infection: influenza, and other viral myositis
- Cardiac, though troponin has superseded CK-MB for this purpose
Rhabdomyolysis
- Classically over 5 times the upper limit; the risk of acute kidney injury rises markedly above 5000 units/l
- The triad is muscle pain, weakness and dark (“tea coloured”) urine
- Urine dipstick positive for blood with no red cells on microscopy is the giveaway, because the dipstick detects myoglobin
- Complications: acute kidney injury, hyperkalaemia, hyperphosphataemia, hypocalcaemia early and hypercalcaemia during recovery, metabolic acidosis, disseminated intravascular coagulation and compartment syndrome
- Management is aggressive intravenous fluid, monitoring of potassium and renal function, and treating the cause
Statin myopathy ranges from myalgia with a normal CK, through myositis, to rhabdomyolysis. Risk is increased by high dose, interacting drugs (macrolides, azoles, ciclosporin, fibrates), hypothyroidism, renal impairment and age.