Rhabdomyolysis

Background

1. Muscle necrosis and the release of intracellular muscle constituents into the circulation

DDx

1. Trauma or muscle compression
   1. Crush injury
   2. Immobilization
   3. Compartment syndrome
2. Nontraumatic exertional
   1. Exercise + hot weather
   2. Exercise + sickle cell
   3. Exercise + hypokalemia
   4. Hyperkinetic states
      1. Seizure
      2. DTs
      3. Stimulant overdose
      4. Malignant hyperthermia
      5. NMS
3. Nontraumatic nonexertional
   1. Drugs and toxins
      1. Coma induced by sedatives
      2. Statins
      3. Colchicine
      4. CO poisoning
   2. Infection
      1. Viral myositis - Influenza, Coxsackie, EBV, HSV, HIV, CMV
      2. Bacterial pyomyositis
      3. Septicemia
   3. Endocrine
      1. Hypothyroidism
   4. Inflammatory myopathies
      1. Moderate CK elevations only (rhabdo only described in case reports)
   5. Miscellaneous
      1. Status asthmaticus
      2. TSS
      3. Mushroom ingestion

Diagnosis

Clinical

1. Myalgias
   1. May progress to weakness
2. Red/brown "tea colored" urine
3. Renal failure

Laboratory

1. Elevated total CK (typically > 10K)
   1. CK-MB may be entirely normal or may be mildly elevated (reflects small amount found in skeletal tissue)
2. Myoglobinuria
   1. UA = +blood, but no RBCs
      1. Sensitivity = 80% (for rhabdo)
   2. Is cleared much faster than CK (may see elevated CK with no myoglobinuria)
   3. Is pathognomonic
3. Transaminitis
4. Creatinine increase (if renal failure)
5. Electrolyte Abnormalities
   1. Hyperkalemia
   2. Hyperphosphatemia
   3. Hypocalcemia
   4. Hyperuricemia
   5. Metabolic acidosis

Treatment

1. Aggressive IVF
   1. Start with 1-2 L/hr
   2. Once diuresis occurs maintain urine output of 200-300 mL/hr
   3. Frequently need ~10 L/day
2. Bicarb?
   1. If IVF establishes diuresis consider adding 75 mmol of NaHCO3 to 1L of 1/2NS
      1. Goal urine pH is > 6.5
      2. Monitor for hypocalcemia closely!
      3. If urine pH is not > 6.5 after 3-4 hrs or symptomatic hypocalcemia results d/c
3. Mannitol?
   1. Consider if unable to establish diuresis with volume repletion
      1. Must check plasma osmolaity and plasma osmolal gap q4-6hr
      2. D/c if osmolal gap > 55 mosmol/kg
4. If mannitol establishes diuresis continue until urine discoloration clears and CK decreases to <10K

Complications

1. Acute Renal Failure
2. Hyperkalemia
3. Hypocalcemia (initial phase)
   1. Treat only if symptomatic or severely hyperkalemic (pts often have rebound hypercalcemia)
4. Hypercalcemia (recovery phase)
5. Hyperphosphatemia

Evidence Based Questions

No randomized, controlled trial has supported the evidence-based use of mannitol, and some clinical studies suggest no beneficial effects. In addition, high accumulated doses of mannitol (>200 g per day or accumulated doses of >800 g) have been associated with acute kidney injury due to renal vasoconstriction and tubular toxicity, a condition known as osmotic nephrosis. However, many experts continue to suggest that mannitol should be used to prevent and treat rhabdomyolysis-induced acute kidney injury and relieve compartmental pressure. During the time mannitol is being administered, plasma osmolality and the osmolal gap (i.e., the difference between the measured and calculated serum osmolality) should be monitored frequently and therapy discontinued if adequate diuresis is not achieved or if the osmolal gap rises above 55 mOsm per kilogram.

A. Bozch X et al. Rhabdomyolysis and Acute Kidney Injury. NEJM 2009; 361: 62-72

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