169 Rhabdomyolysis
Key Points• The most common causes of rhabdomyolysis include substance abuse, direct muscle injury, infection, strenuous physical activity, medications, and toxic ingestions.
• Only 50% of patients with rhabdomyolysis complain of specific muscle symptoms, and less than 10% have muscle tenderness on examination.
• Acute kidney injury is a potential major complication of rhabdomyolysis.
• Aggressive fluid resuscitation decreases the likelihood of kidney injury.
• Rhabdomyolysis and crush syndrome often emerge as the leading causes of delayed mortality in mass casualty incidents involving building collapse.
• Early hemodialysis is indicated when severe hyperkalemia, refractory metabolic acidosis, or crush injury is present.
• Use of supplemental calcium or loop diuretics should be avoided if possible in the setting of rhabdomyolysis.
DefinItion and Epidemiology
Rhabdomyolysis is a condition characterized by injury to skeletal muscle that results in release of the intracellular contents into the extracellular fluid and circulation. Authoritative thresholds for creatine kinase (CK) range between 1000 and 10,000 U/L, but some definitions additionally mandate the presence of myoglobinuria (Box 169.1).
Rhabdomyolysis can occur secondary to trauma, exertion, muscle hypoxia, genetic defects, infections, changes in body temperature, metabolic and electrolyte disorders, drugs and toxins, and idiopathic causes. Various categorizations of rhabdomyolysis have been proposed: traumatic versus atraumatic, reversible versus irreversible, endogenous versus exogenous, and hereditary versus acquired. More than half of all cases of rhabdomyolysis are multifactorial (Box 169.2).
Box 169.2 Causes of Rhabdomyolysis
Rhabdomyolysis afflicts more than 25,000 individuals in the United States each year. Morbidity and mortality vary tremendously depending on etiology, available treatment, time course, and comorbid factors. Acute kidney injury is a potential major complication of rhabdomyolysis and worldwide occurs in 15% to 45% of cases. In contrast, 7% to 10% of cases of acute kidney injury in the United States are caused by rhabdomyolysis.1 Mortality generally ranges from 3% to 10% but can be as high as 25% in mass casualty incidents that involve crush injuries.
Pathophysiology
Rhabdomyolysis is a condition characterized by injury to skeletal muscle that alters the integrity of the cell membrane. Despite the large number of causes of rhabdomyolysis, the underlying pathology involves direct damage to the sarcolemma or depletion of adenosine triphosphate (ATP) within the myocyte resulting in an unregulated increase in intracellular calcium. This leads to constant contraction, energy depletion, and eventual necrosis and death of the muscle cell with release of its intracellular contents into the circulation.2 The most important products released include potassium, phosphorus, myoglobin, CK, aspartate transaminase, alanine transaminase, lactate dehydrogenase, urate, cytokines, and purines.
