Rhabdomyolysis

Rhabdomyolysis is caused by extensive muscle damage, which multiple causes may trigger. Traumatic causes of rhabdomyolysis include a crush injury (e.g., individuals involved in a building collapse); prolonged immobilization due to surgical positioning or hospitalized individuals; high-voltage electrical injuries (e.g., from lightning or power supplies); and severe third-degree burns. Another important cause of rhabdomyolysis is compartment syndrome when increased pressure inside an enclosed anatomical space reduces blood supply and subsequent tissue necrosis. 

Rhabdomyolysis may also occur after strenuous physical activity, especially in untrained individuals and in hot, humid environments that predispose to heat stroke. Impaired heat dissipation from wearing heavy sports equipment increases the risk of rhabdomyolysis. In addition, numerous metabolic or genetic disorders (e.g., inflammatory and metabolic myopathies, glycogen storage disorders, mitochondrial diseases, etc.) also increase the risk of rhabdomyolysis. Other conditions that may lead to rhabdomyolysis include hyperkinetic states, such as seizures, psychomotor agitation; delirium tremens; hyperthermia; viral or bacterial infections; electrolyte disorders, like hypokalemia and hypophosphatemia; use of amphetamines, cocaine, or alcohol; and several medications, including statins, colchicine, and propofol. Certain toxins, such as snake venom, insect venom from wasp and bee stings, and mushroom poisoning, are other known causes of rhabdomyolysis. 

The severity of rhabdomyolysis depends on the extent of muscle damage. The characteristic signs of rhabdomyolysis are muscle pain and weakness, swelling of the affected muscle, and dark urine. Other symptoms may include confusion, fever, vomiting, and abdominal pain. The kidneys filter the massive release of myoglobin from damaged muscle cells, causing renal tubular obstruction, leading to kidney damage. 

Hypovolemia and other electrolyte imbalances, like hyperkalemia, hypocalcemia, hyperuricemia, and acidosis, are also common in rhabdomyolysis. Hyperkalemia may predispose to cardiac arrhythmias, which may be life-threatening. More rarely, the release of prothrombotic substances from damaged muscle cells may lead to disseminated intravascular coagulation (DIC), another life-threatening complication that causes widespread clot formation and platelet depletion. Finally, compartment syndrome is both a cause of and a complication of severe rhabdomyolysis that may arise after fluid resuscitation, with worsening edema of the limb and muscle compartments. 

Diagnosis of rhabdomyolysis is based on clinical presentation and laboratory results. A thorough medical history can help identify and treat the underlying cause. Common lab findings include acute elevation in serum creatine kinase (CK); elevated lactate dehydrogenase (LDH); and electrolyte imbalances, such as hyperkalemia, hyperphosphatemia, hyperuricemia, and metabolic acidosis. CK levels are usually greater than 5,000 UI/L, which is about five times higher than the upper limit of the reference range. A urinalysis is also typically performed to determine the presence of myoglobin in the urine. Myoglobin gives the urine a red-brownish color and may result in a positive result for blood on the urinary dipstick. The false-positive results occur because dipsticks cannot distinguish myoglobin from hemoglobin. However, no red blood cells are typically observed on subsequent urine sediments. 

Additional testing like magnetic resonance imaging (MRI), muscle biopsy, or electromyography (EMG) is not required to diagnose rhabdomyolysis but may be conducted in cases where the underlying diagnosis is uncertain. 

The main goal of rhabdomyolysis treatment is to prevent kidney injury and address any underlying causes when possible. Treatment involves administering intravenous (IV) fluids to maintain adequate urine output and correcting any electrolyte imbalances. In addition, alkalinization of the urine with IV bicarbonate may be done in some instances to decrease the toxicity of myoglobin to the renal tubules. If compartment syndrome is the cause of rhabdomyolysis, surgical treatment with an emergency fasciotomy should be performed promptly, as IV fluid administration may result in worsening edema within the muscle compartment. Hemodialysis may be considered in individuals with low urine output, even with intensive fluid resuscitation, or who have already developed acute kidney failure. 

The prognosis of rhabdomyolysis varies depending on the underlying cause. Nonetheless, most individuals can completely recover kidney function, even if they initially developed acute kidney failure.