Rhabdomyolysis - Differential Diagnosis Framework and Management Summary



Causes of Rhabdomyolysis:

 • Trauma:

	- Immobilization

	- Crush injury

	- Compartment syndrome

	- Electrical injury

 • Exertional:

	- Hyperthermia/Heat exhaustion, Heat injury, Heat stroke

	- Metabolic myopathies

	- Excess exertion/training

	- Seizures

	- Malignant hyperthermia

	- Neuroleptic malignant syndrome

 • Nontraumatic Nonexertional:

	- Electrolytes

	- Toxins

	- Drugs - Statins

	- ETOH

	- Infection - Viral (HIV, Influenza, TSS, Herpes, Coxsackie, etc)

	- Endocrine: Hypo/Hyperthyroidism

	- Autoimmune: Polymyositis/Dermatomyositis



Clinical Features:

 • Triad of symptoms:

	- Muscle pain

	- Weakness

	- Dark urine

 • Other symptoms:

	- Malaise

	- Muscle swelling

	- Fever

	- Tachycardia

	- N/V

	- Abdominal pain



Labs:

 • CPK 5X ULN

 • AST/ALT Elevation 4:1 ratio (AST declines > ALT)

 • AKI: BUN/Cr ↑

 • Aldolase ↑

 • LDH ↑

 • Hyperkalemia

 • Hyperphosphatemia

 • Hypocalcemia/Late - Hypercalcemia

 • Hyperuricemia

 • Hyponatremia

 • HAGMA

 • Late complication: DIC

 • CPK - if doesn’t decline - suspect continued muscle injury or compartment syndrome

 • Myoglobinuria: UA positive for blood with no RBC’s, + myoglobin



AKI Mechanism:

 1. Shift of extracellular fluid into injured muscles - HYPOTENSION → renal vasoconstriction → decreased renal perfusion → renal ischemia

 2. Cast formation: Renal tubular obstruction

 3. Direct myoglobin nephrotoxicity to kidney tubular cells

 4. Heme associated free radicals - oxidative injury



Treatment:

 1. Treatment of underlying disease

 2. Prevent Prerenal azotemia: Isotonic fluid/Lactated ringers

	- Initial rate: 1-2 L/hour with goal urine output: 200 ml/hr

 3. Monitor potassium and calcium several times per day until stable

 4. Loop diuretics for fluid overload

 5. Dialysis for severe hyperkalemia or ATN

 6. Allopurinol for hyperuricemia if levels > 8 mg/dL



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