List the causes, and features of rhabdomyolysis, and outline the principles of management

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College Answer

Aetiology: consider trauma and muscle compression (including immobility), exertional rhabdomyolysis (eg. heat stroke, grand mal seizures), drugs and toxins (via coma/immobility, agitation/hyperthermia, myotoxins eg. HMG-CoA reductase inhibitors, myonecrosis secondary to non-depolarising neuromuscular blockers), infections, inflammatory  myopathies  (eg.  polymyositis),  electrolyte  abnormalities  (esp. hypokalaemia and hypophosphataemia), hyperthermia (eg. malignant hyperpyrexia and neuroleptic malignant syndrome), metabolic myopathies.

Presentation: Consider history of exertion, fitting, drug exposure (including illicit), immobility, family history, and previous episodes.  Patient may complain of painful or weak muscles, and pigmented urine. Investigations reveal markedly elevated muscle enzymes (especially CK), acute oliguric renal failure, and electrolyte abnormalities (hyperkalaemia, hyperphosphataemia, hypocalcaemia, hyperuricaemia and metabolic acidosis).

Principles of management: consider general supportive care, adequate fluid resuscitation, forced alkaline diuresis (including mannitol), specific treatment of underlying cause (eg. dantrolene, phosphate replacement, cooling, removal of precipitants, treatment of infection, fasciotomies etc), and correction of electrolyte abnormalities.

Discussion

The causes of rhabdomyolysis are discussed in Question 26.3 from the second paper of 2013.

A more extensive discussion of rhabdomyolysis can be found among the Required Reading summaries.

To simplify revision, I reproduce the list of differentials below:

Causes of rhabdomyolysis

  • Vascular - muscle ischaemia, eg. ischaemic limb, or myocardial infarction
  • Infectious - eg. necrotising fasciitis
  • Neoplastic, eg. sarcoma
  • Drug-related, eg. due to MDMA or statins, or due to neuroleptic-malignant syndrome
  • Congenital, eg. some sort of congenital myopathy
  • Autoimmune, eg polymyositis or dermatomyositis
  • Traumatic, eg. crush injury, blast injury, compartment syndrome, immobilityetc
  • Environmental, eg. hyperthermic injury, "heat stroke"
  • Endocrine, eg. hyperthyroidism or phaeochromocytoma

Manifestations of rhabdomyolysis

  • Historical features: Trauma, seizures, immobility, drug exposure
  • Symptoms:- muscle pain, decreased mobility, weakness, tea-coloured urine
  • Signs: Muscle compartment swelling, tenderness, weakness, fever
  • Biochemistry: Elevated CK, AST, LDH, urinary myoglobin; renal dysfunction and electrolyte abnormalities (particularly hyperkalemia, hypocalcemia, hyperphosphataemia, hyperuricemia, lactic acidosis)
  • Imaging: CT or MRI evidence of muscle oedema; ultrasound evidence of decreased compartment perfusion

Management of rhabdomyolysis

A recent meta-analysis of management strategies for rhabdomyolysis has presented the following conclusions:

  • Commence IV fluids within 6 hours - as early as possible
  • Aim for a urine output greater than 300ml/hr
  • Use of sodium bicarbonate is only indicated to correct systemic acidosis
  • Use of mannitol is only indicated if urine output >300ml/hr cannot be maintained

Dialysis may be commenced to improve the removal of myoglobin, if a high-permeability membrane filter is available. Even if it is not, standard CVVHDF seems to decrease the risk of renal injury.

References

References

Holt, S., and K. Moore. "Pathogenesis and treatment of renal dysfunction in rhabdomyolysis." Intensive care medicine 27.5 (2001): 803-811.

Vanholder, Raymond, et al. "Rhabdomyolysis." Journal of the American Society of Nephrology 11.8 (2000): 1553-1561.

Bosch, Xavier, Esteban Poch, and Josep M. Grau. "Rhabdomyolysis and acute kidney injury." New England Journal of Medicine 361.1 (2009): 62-72.

Allison, Ronald C., and D. Lawrence Bedsole. "The other medical causes of rhabdomyolysis." The American journal of the medical sciences 326.2 (2003): 79-88.

Brown, Carlos VR, et al. "Preventing renal failure in patients with rhabdomyolysis: do bicarbonate and mannitol make a difference?." Journal of Trauma-Injury, Infection, and Critical Care 56.6 (2004): 1191-1196.

Scharman, Elizabeth J., and William G. Troutman. "Prevention of kidney injury following rhabdomyolysis: a systematic review." Annals of Pharmacotherapy47.1 (2013): 90-105.

Sorrentino, Sajoscha A., et al. "High permeability dialysis membrane allows effective removal of myoglobin in acute kidney injury resulting from rhabdomyolysis." Critical care medicine 39.1 (2011): 184-186.

Tang, Wanxin, et al. "Renal protective effects of early continuous venovenous hemofiltration in rhabdomyolysis: improved renal mitochondrial dysfunction and inhibited apoptosis." Artificial organs 37.4 (2013): 390-400.