Definition of Rhabdomyolysis
Rhabdomyolysis is a clinical syndrome characterized by the rapid breakdown and necrosis of skeletal muscle fibers, resulting in the release of intracellular muscle contents—including creatine kinase (CK), myoglobin, and electrolytes—into the bloodstream and extracellular space. 1, 2, 3
Core Pathophysiologic Features
- The condition involves rupture and necrosis of striated (skeletal) muscle with subsequent leakage of potentially toxic intracellular myocyte contents into the circulation 1, 2
- Released substances include muscle enzymes (particularly CK), myoglobin, and electrolytes, which can cause systemic complications ranging from asymptomatic enzyme elevations to life-threatening acute kidney injury and severe electrolyte abnormalities 2, 3, 4
- Muscle necrosis is the common pathologic factor underlying both traumatic and non-traumatic forms of rhabdomyolysis 3
Clinical Presentation
- The conventional triad of symptoms includes muscle pain, muscle weakness, and dark (red-to-brown) urine due to myoglobinuria 1, 2
- However, clinical presentation varies widely—from completely asymptomatic cases with only laboratory abnormalities to severe disease with life-threatening complications 2, 3
- The American Heart Association notes that clinical symptoms of muscle injury (pain, weakness, or soreness) are key diagnostic elements 5
Diagnostic Criteria
- Creatine kinase (CK) is the biochemical "gold standard" for diagnosis, with elevated CK of at least 5 times the upper limit of normal serving as an important diagnostic marker 1, 6
- Myoglobin is the "gold standard" for prognostication, especially in non-traumatic rhabdomyolysis 1
- Urinalysis showing brown color, cloudiness, and positive for blood without red blood cells (indicating myoglobinuria) is a key diagnostic finding 5
Important Diagnostic Caveat
- CPK alone may not be a sensitive marker in all cases—rare presentations of severe rhabdomyolysis with acute kidney injury and normal CPK at presentation have been documented, with diagnosis confirmed by kidney biopsy showing myoglobin casts 6
- This underscores that clinical suspicion and additional testing (including urinalysis for myoglobinuria) remain essential when rhabdomyolysis is suspected despite normal initial CK levels 6
Spectrum of Severity
- The severity ranges from asymptomatic elevation of muscle enzymes to life-threatening complications including acute kidney injury (occurring in 13-50% of cases), severe electrolyte abnormalities (particularly hyperkalemia), metabolic acidosis, compartment syndrome, and disseminated intravascular coagulation 5, 1, 2
- Myoglobin-induced renal tubular obstruction and toxicity represents the most serious systemic complication and can lead to acute kidney injury requiring dialysis 5