Medical Musing of the Week: Rhabdomyolysis 

Overview

  • Literally means “Disollution of Skeletal muscle”.
  •  The injury to skeletal muscle causing toxic intracellular contents such as myoglobin to leak into plasma

Pathophysiology

  • Inciting injury is of skeletal muscle somehow, how the muscle becomes injured is what’s variable. After the muscle becomes injured myoglobin is released in quantities damaging to the kidney resulting in ischemia and tubular vasoconstriction.  This process results in AKI w/ disturbance in myocardial and calcium hemostasis.
  • Release of intracellular myocyte components
  • Depletion of ATP
  • Increase in proteases, proteolytic enzymes and free O2 radicals-> leading to leakage of potassium, phosphate CK, and myoglobin

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Etiology

  • Crush Injury
  • Snake venom
  • Orthopedic trauma (be sure to r/o compartment syndrome
  • Immobilization and hypovolemia
  • Infection (Most common infectious cause are Influenza A&B)
  • Genetic muscle defects (those which cause a ATP supply and demand mismatch)
  • Hyperthermia
  • Low phosphorus and potassium
  • Propofol is the most common drug that will cause Rhabdomyolysis in children
  • Exertional Activity aka working out too hard (sickle cell patients are at increased risk of rhabdo d/t exercise

Clinical Manifestations

  • Classic Triad (presents less frequently in children) Tea colored urine, myalgia and generalized fatigue
  • History: to determine cause meds/trauma/infection/ETOH/drugs.  Individuals who have started new exercise program.  Esp if they were prior athletes (increased risk)
  • PE: edema (esp if unilateral)
  • Decreased strength
  • Skin changes consistent with necrosis
  • Hyper/hypothermia
  • MC muscle group injured in adults are calves and lower back

Diagnosis

  • CK levels are the most reliable/check q6-q12h/rise within 12 hours/peak 24-36/should decrease approximately 30% per day with treatment
  • Myoglobin: if negative does not rule out, can have false negative because will clear system in 6 hours/ if positive he atria can get myoglobin urine assay
  • EKG to look for changes due to electrolyte abnormalities
  • UA is WNL in >50% of patients and therefore is not a reliable measure

Treatment

  • ABCs
  • IVF resuscitation–aggressive as long as EF is intact 2-3L bolus and maintain at 100-200cc/hr
  • Activity restriction-no aggressive exercise
  • Electrolyte replacement as needed (keep mag >2.0 and K >4.0–cardiac

Complications

  • Compartment Syndrome
  • Decreased albumin
  • Hyperurecemia
  • DIC

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