Rhabdomyolysis

Question 1

Define rhabdomyolysis.

Answer 1

Rhabdomyolysis is the end result of any disease process that causes muscle cell (myocyte) lysis.

Question 2

What is the pathophysiology of rhabdomyolysis?

Answer 2

Result of traumatic or medical damage to the sarcolemma (myocyte cell membrane) of skeletal muscle cells
There is subsequent release of intracellular ions, myoglobin, CK and urates results in:

• electrolyte disturbances
• acidaemia
• DIC
• AKI
• multi-organ failure

Question 3

What is the diagnostic criterion for rhabdomyolysis?

Answer 3

CK 5 times the upper limit of normal or > 1000 IU/L

Question 4

How common is rhabdomyolysis?

Answer 4

Some degree of rhabdomyolysis among 85% of critically injured patients admitted to trauma ITU

Question 5

What are the causes of rhabdomyolysis?

Answer 5

• Traumatic or medical destruction of muscle fibres:
• Trauma
• Muscle ischaemia
• Vascular injuries
• Inherited muscle enzyme disorders
• Seizures
• Infections
• Metabolic abnormalities

Drugs:

• Cocaine, amphetamines
• Narcotics and CNS depressants
• Salicylate toxicity
• Diuretics due to potassium depletion
• Statins
• Antipsyhotics
• Antidepressants (sertraline, venlafaxine)
• DPP4 inhibitors

Question 6

What are the clinical features of rhabdomyolysis?

Answer 6

• Muscle weakness
• Pain/tenderness
• Swelling of the affected body region
• Check for any signs of compartment syndrome
• General malaise
• Dark urine - due to urinary myoglobin

Question 7

What investigations should you do in rhabdomyolysis?

Answer 7

CK - levels 5 times limit of normal or over 1000 IU/L
Urinalysis
FBC, U&Es, uric acid, coagulation profile , LFTs
TSH - rule out as cause
ESR - screen for inflammatory myopathy
ANA - screen for autoimmune disease
Muscle biopsy - only indicated if genetic aetiology suspected

Question 8

How do you manage rhabdomyolysis?

Answer 8

Aggressive rehydration - promotes clearance of intracellular muscular toxins; 400ml/hr and monitoring urine output

Other:

+/- Sodium bicarbonate - started by a specialist only; alkalinises the urine and prevents crystallisation of uric acid
+/- Diuretic - little evidence for this
Monitor and treat hyperkalaemia - potassium > 6mmol/L requires cardiac monitoring; treat with insulin and glucose infusions, and calcium gluconate to protect the heart
Dialysis - in AKI with intractable hyperkalaemia, hypervolaemia or metabolic acidosis

Question 9

What are the complications of rhabdomyolysis?

Answer 9

• AKI
• Electrolyte abnormalities
• Compartment syndrome
• DIC
• Multisystem failure

Question 10

What is the prognosis with rhabdomyolysis?

Answer 10

Most make a complete recovery
Permanent damage is rare