rhabdomyolysis

rhabdomyolysis
Name	Rhabdomyolysis
Synonyms	Rhabdo
Field	Emergency medicine, Nephrology, Toxicology
Symptoms	Muscle pain, Weakness, Dark urine
Complications	Acute kidney injury, Hyperkalemia, Compartment syndrome
Causes	Trauma (medicine), Statin, Exertion, Genetic disorders
Diagnosis	Creatine kinase, Myoglobinuria, Electrolyte imbalance
Treatment	Intravenous therapy, Renal replacement therapy, Alkalinization
Prognosis	Variable, depends on kidney involvement

rhabdomyolysis. It is a serious syndrome resulting from the rapid breakdown of skeletal muscle tissue, leading to the release of intracellular contents into the systemic circulation. This process can cause life-threatening complications, most notably acute kidney injury, due to the nephrotoxicity of muscle components like myoglobin. The condition is managed by specialists in emergency medicine and nephrology, often requiring urgent intervention to prevent mortality.

Definition and pathophysiology

The fundamental pathophysiological event is necrosis of skeletal muscle fibers, which compromises the integrity of the sarcolemma. This disruption allows intracellular constituents, including myoglobin, creatine kinase, potassium, and phosphate, to leak into the interstitial fluid and subsequently the blood plasma. Myoglobin, a protein that normally facilitates oxygen transport in muscle, is freely filtered by the glomerulus but can precipitate in the renal tubule, especially in an acidic environment, leading to cast formation and obstruction. Furthermore, the release of intracellular potassium can precipitate severe hyperkalemia, which may cause fatal cardiac arrhythmia. The process also triggers a systemic inflammatory response syndrome, contributing to multiple organ dysfunction syndrome.

Causes and risk factors

Etiologies are broadly categorized into traumatic, non-traumatic exertional, and non-exertional causes. Major traumatic causes include crush injury, as historically documented in victims of events like the London Blitz, and compartment syndrome. Exertional causes encompass intense physical activity, such as marathon running or military training, particularly in hot climates like those encountered during operations in Iraq. Non-exertional causes are numerous and include pharmacological agents like statins, antipsychotics (e.g., associated with neuroleptic malignant syndrome), and substances of abuse including cocaine and alcohol. Other significant risk factors are inherited metabolic myopathies such as McArdle disease, infections like influenza and Legionnaires' disease, electrolyte disturbances (e.g., hypokalemia), and hyperthermia from conditions like malignant hyperthermia or heat stroke.

Signs and symptoms

The classic triad consists of muscle pain, weakness, and dark urine, though this complete presentation is not universal. Myalgia typically affects large muscle groups such as the thighs, calves, and lower back. Weakness may be profound and localized. The hallmark finding of dark urine, often described as cola-colored, is due to myoglobinuria. Systemic signs can include malaise, fever, and nausea. Severe complications may manifest as edema and pain suggestive of compartment syndrome, or symptoms of uremia and fluid overload if acute kidney injury develops. Hyperkalemia may present with palpitations or cardiac arrest.

Diagnosis

Diagnosis is primarily biochemical, centered on a markedly elevated serum creatine kinase level, often exceeding 5 times the upper limit of normal. The detection of myoglobin in the urine, or myoglobinuria, is supportive but not always present. Urinalysis typically shows a positive dipstick test for blood without a corresponding number of red blood cells on microscopy, indicative of pigment nephropathy. Essential blood tests include a complete blood count, basic metabolic panel to assess for hyperkalemia, hyperphosphatemia, hypocalcemia, and renal function tests like blood urea nitrogen and creatinine. Investigations like electromyography are rarely needed, while magnetic resonance imaging may help assess muscle edema and necrosis.

Treatment and management

Immediate management focuses on aggressive intravenous therapy with crystalloid solutions, typically normal saline, to restore renal perfusion and promote diuresis, aiming to flush myoglobin from the renal tubules. Alkalinization of urine with sodium bicarbonate is sometimes employed, though evidence is debated, to prevent myoglobin precipitation. Critical complications require specific interventions: hyperkalemia is treated with insulin, glucose, calcium gluconate, and possibly sodium polystyrene sulfonate or renal replacement therapy. Established acute kidney injury often necessitates hemodialysis or continuous renal replacement therapy. Compartment syndrome is a surgical emergency requiring fasciotomy. Underlying causes must be addressed, such as discontinuing offending medications like simvastatin or treating underlying infections.

Prognosis and complications

Prognosis is generally favorable with prompt treatment, but mortality increases significantly with the development of major complications. The most serious acute complication is acute kidney injury, which occurs in up to a third of cases and may require temporary or permanent dialysis. Hyperkalemia poses a direct risk of cardiac arrest. Other potential sequelae include disseminated intravascular coagulation due to thromboplastin release, and compartment syndrome which can lead to Volkmann's contracture and permanent disability. Long-term outcomes for survivors of severe episodes depend on the extent of renal recovery and any residual muscle damage.

Category:Medical emergencies Category:Nephrology Category:Muscle disorders