Rhabdomyolysis

In our Morning Report at WCH this week, we discussed an approach to the evaluation of myalgias and elevated creatine kinase (CK) levels.

Learning Points:

  1. Causes of myalgias
  2. Differential diagnosis of rhabdomyolysis
  3. Preliminary work-up
  4. Electrolyte disturbances seen in rhabdomyolysis
  5. Management basics for rhabdomyolysis

Differential Diagnosis of Myalgias:

  • may be focal or generalized
    • focal: trauma, pyomyositis, myofascial pain syndrome, muscle infarction, compartment syndrome
    • generalized:
      • Infection
      • Autoimmune: PMR, Poly/dermatomyositis, RA, SLE, Spondylarthropathy
      • Endocrine: Hypothyroidism, Adrenal insufficiency
      • Medication: statins, many others
      • Psychiatric
      • Noninflammatory pain syndromes: Fibromyalgia, Chronic Fatigue Syndrome

Differential Diagnosis of Rhabdomyolysis:

  • Rhabdomyolysis = muscle necrosis + release of intracellular components from within muscle
    • kind of like “tumor lysis” but from a muscle!
      • Physiology is similar:
        • Release of K, phosphate, uric acid, LDH
        • Also release of myoglobin which does not have a binding-molecule like hemoglobin (haptoglobin)

Rhabdo.png

Suggested preliminary investigations:

  • For the evaluation of a muscle complaint or suspected rhabdomyolysis:
    • CBC (look for infection)
    • Coagulation markers (DIC may coexist)
    • Lytes, Extended lytes, Uric Acid
    • AST, ALT, ALP, Tbili with LDH and CK, trop
    • Creatinine, urea, urinalysis, urine myoglobin
    • Urine microscopy-hemegranular (‘muddy brown’) casts in acute tubular necrosis (ATN)
    • Tox screen
    • Consider ESR, CRP, ANA, ENA (anti Jo-1)
    • Pertinent infectious work-up if suspected (i.e. Throat swabs, NP swab, blood cultures, sputum, etc)

Electrolyte abnormalities in rhabdomyolysis:

rhabdo-table

Management Principles:

  • Major therapeutic aims:
    • target and maintain euvolemia
    • Prevent/limit renal injury relating to myoglobinuria
  • IV fluid resuscitation
    • increasing urine output limits cast formation and promotes potassium excretion
    • can consider use of sodium bicarbonate infusion to achieve forced alkaline diuresis (pH>6.5) though there is no clear evidence of benefit
      •  Bicarb infusion ‘recipe’: 3 amps of NaHCO3 in 850 cc of D5W
  • Diuretics
    • theoretically to enhance urine output and prevent precipitation in renal tubules
    • Neither mannitol or lasix of clear-evidence of benefit

Additional Clinical Pearls:

  • Influenza is a common cause of elevated CK levels/myositis
  • A positive urine dip for blood but absence of red blood cells on urine microscopy is suggestive of myoglobinuria
  • Elevated CK levels can be multifactorial; an inciting trigger (drug/infection) might unmask an underlying muscle/mitochondrial disorder

Further Reading:

  1. Chatzizisis, YS et al. The syndrome of rhabdomyolysis: Complications and treatment. European Journal of Internal Medicine. 2008; 19:568-574.
  2. Giannoglou, GD. The syndrome of rhabdomyolysis: Pathophysiology and Diagnosis. European Journal of Internal Medicine. 2007; 18: 90-100.

 

 

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