Rhabdomyolysis

Normal skeletal muscle function is dependent on appropriate electrolyte exchange, adequate metabolism of adenosine triphosphate (ATP), and intact plasma membrane of the myocytes. In rhabdomyolysis, these processes are disrupted, resulting in the breakdown of skeletal muscle. Destruction of skeletal muscle tissue leads to release of the intracellular components of myocytes into the plasma, including creatine kinase (CK), myoglobin, and various electrolytes. Myoglobinuria and electrolyte abnormalities cause end-organ complications, including acute kidney injury Acute Kidney Injury (AKI) Acute kidney injury is a rapid decrease in renal function over days to weeks, causing an accumulation of nitrogenous products in the blood (azotemia) with or without reduction in amount of urine... read more .

Any form of muscle damage can theoretically result in rhabdomyolysis. The most common etiologies include

Less common etiologies include

The classic triad of symptoms in rhabdomyolysis is muscle pain, weakness, and reddish-brown urine. However, this trio of symptoms is present in fewer than 10% of all patients with rhabdomyolysis.

Clinical presentation is variable, and many patients have no muscle complaints at all. When present, muscle pain affects proximal muscle groups, such as shoulders, thighs, lower back, and calves. At a high concentration, myoglobin excreted into the urine changes its color to red or brown and can be assessed with a dipstick analysis positive for blood (caused by myoglobinuria). However, due to rapid excretion of myoglobin, rhabdomyolysis cannot be excluded in the absence of myoglobinuria or urine discoloration.

Other signs and symptoms vary based on the inciting event and complications (eg, fever is present in patients with infection and altered mental status in cases of intoxication).

Acute kidney injury is reported in 15 to 50% of rhabdomyolysis complications (1 Symptoms and signs reference Rhabdomyolysis is a clinical syndrome involving the breakdown of skeletal muscle tissue. Symptoms and signs include muscle weakness, myalgias, and reddish-brown urine, although this triad is... read more ), and is higher in patients with concurrent dehydration, sepsis, and creatine kinase level over 15,000 IU/L (250 mckat/L).

Rhabdomyolysis is suspected based on history, clinical signs, and symptoms. Confirmation is by laboratory testing of elevated CK. Although a cutoff threshold has not been established, a CK level of > 5 times the upper limit of normal is typically required for diagnosis.

Other corroborating laboratory testing includes the presence of myoglobin in urine, particularly if microscopic urine examination shows no red blood cells. Myoglobinuria is detected when urinary myoglobin exceeds 250 mcg/mL. Other laboratory features include rapidly rising serum creatinine, hyperkalemia Hyperkalemia Hyperkalemia is a serum potassium concentration > 5.5 mEq/L (> 5.5 mmol/L), usually resulting from decreased renal potassium excretion or abnormal movement of potassium out of cells. There... read more , hyperuricemia, hypocalcemia Hypocalcemia Hypocalcemia is a total serum calcium concentration < 8.8 mg/dL (< 2.20 mmol/L) in the presence of normal plasma protein concentrations or a serum ionized calcium concentration < 4... read more , or hypercalcemia Hypercalcemia Hypercalcemia is a total serum calcium concentration > 10.4 mg/dL (> 2.60 mmol/L) or ionized serum calcium > 5.2 mg/dL (> 1.30 mmol/L). Principal causes include hyperparathyroidism... read more , hyperphosphatemia Hyperphosphatemia Hyperphosphatemia is a serum phosphate concentration > 4.5 mg/dL (> 1.46 mmol/L). Causes include chronic kidney disease, hypoparathyroidism, and metabolic or respiratory acidosis. Clinical... read more , lactic acidosis Lactic Acidosis Lactic acidosis is a high anion gap metabolic acidosis due to elevated blood lactate. Lactic acidosis results from overproduction of lactate, decreased metabolism of lactate, or both. (See also... read more , and thrombocytopenia Overview of Platelet Disorders Platelets are circulating cell fragments that function in the clotting system. Thrombopoietin helps control the number of circulating platelets by stimulating the bone marrow to produce megakaryocytes... read more .

In general, treatment is supportive along with treatment of cause and of any resulting complications.

Supportive treatment includes intravascular expansion with IV fluids to prevent acute kidney injury Acute Kidney Injury (AKI) Acute kidney injury is a rapid decrease in renal function over days to weeks, causing an accumulation of nitrogenous products in the blood (azotemia) with or without reduction in amount of urine... read more as well as other supportive treatments (eg, mechanical ventilation in cases of acute respiratory failure Acute Hypoxemic Respiratory Failure (AHRF, ARDS) Acute hypoxemic respiratory failure is defined as severe hypoxemia (PaO2 (See also Overview of Mechanical Ventilation.) Airspace filling in acute hypoxemic respiratory failure (AHRF) may result... read more ). There is no clear evidence of benefit of urinary alkalinization with sodium bicarbonate, which is particularly contraindicated in cases of alkalosis Metabolic Alkalosis Metabolic alkalosis is primary increase in bicarbonate (HCO3⁻) with or without compensatory increase in carbon dioxide partial pressure (Pco2); pH may be high or nearly normal. Common... read more or hypocalcemia Hypocalcemia Hypocalcemia is a total serum calcium concentration < 8.8 mg/dL (< 2.20 mmol/L) in the presence of normal plasma protein concentrations or a serum ionized calcium concentration < 4... read more .

If the inciting event is due to a compartment syndrome Compartment Syndrome Compartment syndrome is increased tissue pressure within a closed fascial space, resulting in tissue ischemia. The earliest symptom is pain out of proportion to the severity of injury. Diagnosis... read more , early fasciotomy is done in addition to supportive therapy. Infections are treated with appropriate antimicrobial agents. Any potential inciting drugs (eg, statins) are discontinued. Electrolyte disturbances are corrected.

Complications such as acute kidney injury are treated with IV fluids and sometimes hemodialysis Hemodialysis In hemodialysis, a patient’s blood is pumped into a dialyzer containing 2 fluid compartments configured as bundles of hollow fiber capillary tubes or as parallel, sandwiched sheets of semipermeable... read more . Disseminated intravascular coagulation Disseminated Intravascular Coagulation (DIC) Disseminated intravascular coagulation (DIC) involves abnormal, excessive generation of thrombin and fibrin in the circulating blood. During the process, increased platelet aggregation and coagulation... read more is treated with fresh frozen plasma.