Malignant hyperthermia is an inherited disease that causes a rapid rise in body temperature (fever) and severe muscle contractions when the affected person receives general anesthesia.

This condition is not the same as hyperthermia due to medical emergencies such as heat stroke.

Malignant hyperthermia is an autosomal dominant trait, meaning it requires only one parent carrying the disease for a child to inherit the condition. It may be associated with muscular diseases such as multiminicore myopathy and central core disease.

One form of malignant hyperthermia is caused by a defect in the ryanodine receptor (RYR1) gene

Malignant hyperthermia is often noted for the first time after a patient is given anesthesia during a surgical procedure.

Symptoms include:

• Rapid rise in temperature to 105 degrees F or higher
• Muscle rigidity and stiffness
• Dark brown urine
• Muscle ache without obvious exercise to explain sore muscles

There may be a family history of malignant hyperthermia or unexplained death during anesthesia.

Tests that may be done include:

• Chem-20
• Genetic testing to look for defects in the RYR1 gene
• Muscle biopsy
• Myoglobin in the urine

For an episode of malignant hyperthermia, a cooling blanket can help reduce fever. The use of a drug called dantrolene during episodes of malignant hyperthermia has greatly reduced the number of deaths.

Fluids given by IV and mouth, as well as certain medications, are essential for maintaining kidney function during an acute episode.

Malignant Hyperthermia Association of the United States - www.mhaus.org

Repeated episodes or untreated episodes can cause kidney failure. Untreated episodes can be fatal.

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

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.

If you or anyone in your family has malignant hyperthermia, it is very important to tell your doctor, especially before having surgery with general anesthesia. The use of appropriate anesthetic medication can prevent the complications of malignant hyperthermia during surgery.

It is important to avoid stimulant drugs such as cocaine, amphetamine (speed) and ecstasy 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.

Vicario S. Heat illness. In: Marx J, ed. Rosen’s Emergency Medicine: Concepts and Clinical Practice. 6th ed. St. Louis, Mo: Mosby; 2006:chap 139.