Rhabdomyolysis

Rhabdomyolysis is a condition caused by muscle cell necrosis. As muscle cells die, their contents are released into the bloodstream. This includes the release of myoglobin, potassium and creatine kinase (CK), along with other substances.

A high level of myoglobin in the blood is toxic to the kidneys (nephrotoxic). Normally, the kidneys are able to remove small amounts of myoglobin from the blood, by excreting it into the urine. Rhabdomyolysis causes a sudden and excessive rise in the myoglobin level, which the kidney may not be able to excrete adequately. High levels of myoglobin are toxic to the kidney and can cause acute kidney injury.

A high level of potassium in the blood (hyperkalemia) is dangerous. Normally the kidney removes excess potassium, by excreting it into the urine. Rhabdomyolysis causes a sudden and excessive rise in the potassium level, which the kidney may not be able to excrete adequately. Furthermore, if there is acute kidney injury present (due to the nephrotoxic effect of myoglobin), then this will significantly hinder the excretory ability of the kidney.

Causes
Muscle cell necrosis can be caused by a variety of events. Some examples are:

• Crush injury - such as being trapped under a collapsed structure
• Prolonged immobility on a hard surface – such as incapacitating stroke or fractured hip, or coma following a drug overdose
• Excessive physical exertion – particularly in the untrained individual
• Heat stoke – severe hyperthermia, such as a body temperature exceeding 40 degrees
• Compartment syndrome – swelling within a muscle compartment, most commonly seen in the lower leg after a tibial fracture
• Electrical injury - either from high voltage power supply or from lightening
• Extensive full thickness burns
• Prolonged convulsion – from prolonged and frequent muscle contractions that take place during a tonic-clonic seizure
• Snake bite – certain snake bites that cause tissue necrosis 

Signs and Symptoms
Rhabdomyolysis can cause muscle weakness, muscle pain and dark colored urine. The dark urine is myoglobin that has been excreted by the kidneys into the urine. However, presentations vary, and these three findings are not always present.

There may also be signs and symptoms related to the underlying cause. For example, a prolonged period of immobility may have produced discoloration of the skin, or heat stroke may reduce the patient’s level of consciousness.

Complications
Acute kidney injury and high potassium levels (hyperkalemia) are the most common complications of rhabdomyolysis. Acute kidney injury can result in high levels of urea (uremia), volume overload and metabolic acidosis. High potassium levels (hyperkalemia) can cause life-threatening cardiac arrhythmias.

Rhabdomyolysis can also cause abnormal levels of other substances in the blood, such as elevated uric acid levels (hyperuricemia), or decreased calcium levels (hypocalcemia). During recovery however, the calcium level may become elevated (hypercalcemia).

Rare Complications
A less frequent complication of rhabdomyolysis is the development of swelling in the damaged muscles, which may then lead to compartment syndrome.

Another less frequent complication of rhabdomyolysis is disseminated intravascular coagulation (DIC), caused by certain enzymes being released from the damaged muscle into the bloodstream. 

Investigations
Some laboratories are able to measure levels of creatine kinase (CK) or myoglobin in the blood, making diagnosis easy. However, if this is unavailable then a clinical diagnosis must be made. Clinical diagnosis is made by taking a detailed history from the patient or relative, and performing a thorough physical examination.

Blood tests for kidney function (creatinine and urea) should be performed, to assess for acute kidney injury.

Blood tests should also include electrolyte levels, especially potassium levels. An electrocardiogram (ECG) can be performed to assess for conduction abnormalities associated with high potassium levels (hyperkalemia).

Treatment
The main aim of treatment is to preserve kidney function. This is done by giving generous amounts of intravenous 0.9% sodium chloride (normal saline). Intravenous fluids containing potassium (such as ringers lactate) must be avoided.

Fluid input and output should be recorded. In severe cases a urinary catheter might be advised to enable regular and accurate monitoring of the urine output.

Electrolyte abnormalities may require treatment. High potassium levels (hyperkalemia) need to be treated urgently. Treatment may include intravenous glucose and insulin, salbutamol nebulizers and intravenous sodium bicarbonate. Intravenous calcium (such as calcium gluconate) should also be administered for hyperkalemia, as it offers some protection to the heart from arrhythmias.

Low calcium levels (hypocalcemia) do not usually need to be treated, as rebound high calcium levels (hypercalcemia) is common during recovery. Regardless, if hyperkalemia is present, then calcium can be administered. 

Dialysis may be required for patients who have developed acute kidney injury, and who have severe hyperkalemia, pulmonary edema, metabolic acidosis or uremia.

Since there are many potential causes of rhabdomyolysis, it is necessary to also investigate and treat the specific underlying cause.