Rhabdomyolysis

Question 1

Define rhabdomyolysis.

Answer 1

Traumatic or medical injury to the sarcolemma (the myocyte cell membrane) of the skeletal muscle cells causing release of intracellular ions, myoglobin, creatine kinase (CK), and urates into the circulation –> electrolyte disturbances, acidaemia, DIC, renal failure, and multi-organ failure.

Question 2

What are the causes of rhabdomyolysis?

Answer 2

• seizure
• collapse/coma (e.g. elderly patients collapses at home, found 8 hours later)
• ecstasy
• crush injury
• McArdle’s syndrome
• drugs: statins (especially if co-prescribed with clarithromycin)

Question 3

What antibiotics should not be co-prescribed with statins?

Answer 3

Clarithromycin

Question 4

What are the investigation findings in rhabdomyolysis?

Answer 4

• acute kidney injury with disproportionately raised creatinine
• elevated CK
• myoglobinuria
• hypocalcaemia
• elevated phosphate (released from myocytes)
• hyperkalaemia (may develop before renal failure)
• metabolic acidosis

Question 5

What CK level is diagnostic of rhabdomyolysis?

Answer 5

The measurement of serum CK levels at more than 5 times the upper limit of normal is used as diagnostic criterion.

Question 6

What are the signs/symptoms of rhabdomyolysis?

Answer 6

• Muscular pain and tenderness (e.g. after recent crush injury or prolonged immobilisation)
• General malaise
• Dark urine due to myoglobin*

NB:* Other causes of red urine include ingestion of beetroot, blackberries, and rhubarb and use of medications such as senna, doxorubicin, and phenothiazines

Question 7

What is the cause of hypocalcaemia in rhabdomylosis?

Answer 7

Myoglobin binds calcium

Question 8

What is the management of rhabdomyolysis?

Answer 8

1. Hydration therapy - preventative therapy
2. Urine alkalinisation - myoglobin is toxic to renal tubules in acidic urine, pH >6 may be protective
3. Diuretics - lack of evidence

If anuric or unresponsive then haemodialysis.

Question 9

What are the complications of rhabdomyolysis?

Answer 9

1. Acute renal failure - UO must be strictly monitored to ensure renal perfusion and adequacy of therapy
2. Electrolyte abnormalities - continuous cardiac telemetry with frequent electrolyte sampling should be performed to detect and anticipate cardiac rhythm disturbances.
3. Compartment syndrome (although this may be the cause)
4. DIC - due to release of activating substances
5. Multisystem failure