Alternative names 
Malignant hyperthermia; Hyperpyrexia - malignant

Definition
Malignant hyperthermia is a group of inherited muscle problems characterized by muscle breakdown following certain stimuli - such as anesthesia, extremes of exercise (particularly in hot conditions), fever, or use of stimulant drugs. The problems associated with this condition result from over-excitable muscles that contract uncontrollably, severe fever, abnormal heart rhythms, and kidney failure.

Causes, incidence, and risk factors

Malignant hyperthermia is inherited as an autosomal dominant trait (it requires only one affected parent for a child inherit the condition). It may be associated with muscular diseases such as muscular dystrophy and central core disease.

Malignant hyperthermia is often noted for the first time during administration of anesthesia. The anesthetized patient rapidly develops a high fever and muscle rigidity. During these episodes, muscle tissue is destroyed and break-down products of muscle may damage the kidneys and cause acute renal failure. The urine may turn dark due to released muscle pigments (see rhabdomyolysis).

Malignant hyperthermia can be fatal if not treated immediately. It can be prevented by administration of appropriate drugs before anesthesia.

Symptoms

 
• Rapid rise in temperature following administration of anesthesia  
• Muscle rigidity and stiffness following administration of anesthesia  
• Dark brown coloration to urine  
• Muscle ache without obvious exercise to explain sore muscles  
• Family history of malignant hyperthermia or unexplained death during anesthesia

Signs and tests

 
• Blood chemistry (see chem-20) shows increased blood levels of creatine phosphokinase (CPK), potassium, uric acid, phosphate.  
• Myoglobin in the urine is elevated.  
• Muscle biopsy using an in vitro contracture test may show abnormal results in response to certain drugs such as caffeine and halothane (an anesthetic).  
• Muscle biopsy may show abnormal muscle, such as central cores, in some types.  
• Genetic testing such as ryanodine receptor (RYR1) may show gene abnormalities.  
• Phosphorus magnetic resonance spectroscopy, a research test, may show abnormal muscle function.

Treatment
The best course of action for this condition is prevention. If a general anesthetic is to be given, pretreatment with dantrolene sodium is recommended. If you have a family history of anesthesia-induced problems it is imperative to alert your surgeon and anesthesiologist.

For an episode of malignant hyperthermia, antipyretics (fever-reducing medications such as acetaminophen) and a cooling blanket can help reduce acute fever.

Intravenous and oral fluids as well as certain medications are essential for maintaining kidney function during an acute episode.

Expectations (prognosis)
Episodes of the disorder can often be prevented. Repeated episodes or untreated episodes can cause kidney failure. Untreated episodes can be fatal. Fortunately, the use of the drug dantrolene has made fatalities much less common.

Complications

 
• Rhabdomyolysis, a kidney injury caused by excess myoglobin  
• Renal failure  
• Myopathy (weak muscles) or muscular dystrophy  
• Death

Calling your health care provider
If you know that you or a member of your family has had problems with general anesthesia, or if you know you have a family history of malignant hyperthermia, be sure to notify both the surgeon and the anesthesiologist before having any surgery.

Prevention

It is important to recognize susceptible patients before giving them anesthesia. Clues may be obtained from the family history or previous episodes. Episodes of malignant hyperthermia may be prevented by giving dantrolene sodium before anesthesia.

It is important to avoid stimulant drugs such as cocaine, amphetamine (speed) and ecstasy (an amphetamine derivative) as they may produce malignant hyperthermia-like problems in susceptible individuals.

Genetic counseling is recommended for anyone with a family history of myopathy, muscular dystrophy or malignant hyperthermia.

Medical Encyclopedia

All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.