Causes and Risks: Myoglobin is an iron-containing pigment found in the skeletal muscle. When the skeletal muscle is damaged, the myoglobin is released into the bloodstream. It is filtered out of the bloodstream by the kidneys. Myoglobin may occlude the structures of the kidney, causing damage such as acute tubular necrosis or kidney failure. Myoglobin breaks down into potentially toxic compounds, which will also cause kidney failure. Necrotic (dead tissue) skeletal muscle may cause massive fluid shifts from the bloodstream into the muscle, reducing the relative fluid volume of the body and leading to shock and reduced blood flow to the kidneys.

The disorder affects about 1 out of 10,000 people of any age, sex, and race. It may be caused by any condition that results in damage to skeletal muscle, especially trauma.

Risk factors include:

• severe exertion such as marathon running or calisthenics
• ischemia or necrosis of the muscles (as may occur with arterial occlusion, deep venous thrombosis, or other conditions)
• seizures
• use or overdose of drugs-especially cocaine, amphetamines, heroin, or PCP
• trauma
• shaking chills
• heat intolerance and/or heatstroke
• alcoholism (with subsequent muscle tremors)

Prevention: After any condition that may involve damage to skeletal muscle, hydration should be adequate to dilute the urine and flush the myoglobin out of the kidney. (See "Treatment".)

Symptoms:

• abnormal urine color (dark, red, or cola colored)
• muscle tenderness
• weakness of the affected muscle(s)
• generalized weakness
• muscle stiffness or aching (myalgia)

• weight gain (unintentional)
• seizures
• joint pain
• fatigue

Signs and Tests: An examination reveals tender or damaged skeletal muscles.

• A urinalysis may reveal casts and hemoglobin without formed red blood cells.
• A urine myoglobin test is positive.
• A serum myoglobin test is positive.
• A CPK is very high.
• A serum potassium may be very high (potassium is released from cells into the bloodstream when there is cell breakdown).

• creatinine - urine
• creatinine
• CPK isoenzymes

Treatment: Early and aggressive hydration may prevent complications by rapidly eliminating the myoglobin out of the kidneys. The hydration needs with muscle necrosis may approximate the massive fluid volume needs of a severely burned patient. This may involve intravenous administration of several liters of fluid until the condition stabilizes.

Diuretic medications such as mannitol or furosemide may aid in flushing the pigment out of the kidneys. If the urine output is sufficient, bicarbonate may be given to maintain an alkaline urine state. This helps to prevent the dissociation of myoglobin into toxic compounds.

Hyperkalemia should be treated if present. Kidney failure should be treated as appropriate.

Prognosis: The outcome varies depending on the extent of kidney damage incurred.

Complications:

• acute tubular necrosis
• acute renal failure

Call your health care provider if symptoms indicate rhabdomyolysis may be present.