Hyperthermia - malignant; Hyperpyrexia - malignant; MH
Malignant hyperthermia (MH) is a disease that causes a fast rise in body temperature and severe muscle contractions when someone receives general anesthesia with one or more of the following drugs: halothane, isoflurane, sevoflurane, desflurane or succinylcholine. MH is a genetic disorder passed down through families.
Hyperthermia means high body temperature. Malignant hyperthermia is not the same as hyperthermia from other medical emergencies such as heat stroke or infection.
MH is inherited. Only one parent has to carry the gene for the disease for a child to inherit the condition.
It may occur with some other inherited muscle diseases, such as multiminicore myopathy and central core disease.
Symptoms of MH include:
- Dark brown urine (due to a muscle protein called myoglobin in the urine)
- Muscle ache without an obvious cause, such as exercise or injury
- Muscle rigidity and stiffness
- Rise in body temperature to 105°F (40.6°C) or higher
Exams and Tests
MH is often discovered after a person is given anesthesia during surgery.
There may be a family history of MH or unexplained death during anesthesia.
The person may have a fast and often irregular heart rate.
Tests for MH may include:
- Blood clotting studies (PT, or prothrombin time; PTT, or partial thromboplastin time)
- Blood chemistry panel, including CK (creatinine kinase, which is higher in the blood when muscle is destroyed during a bout of the illness)
- Genetic testing to look for defects in the genes that are linked with the disease
- Muscle biopsy
- Urine myoglobin (testing for muscle protein in the urine)
During an episode of MH, a medicine called dantrolene is often given. Wrapping the person in a cooling blanket can help reduce fever and the risk for serious complications.
To preserve kidney function during an episode, the person may receive fluids through a vein.
These resources can provide more information about MH:
- Malignant Hyperthermia Association of the United States --
- National Organization for Rare Disorders --
- US National Library of Medicine - MedlinePlus website --
Repeated or untreated episodes can cause kidney failure. Untreated episodes can be fatal.
These serious complications can occur:
- Breakdown of muscle tissue
- Swelling of the hands and feet and problems with blood flow and nerve function (compartment syndrome)
- Abnormal blood clotting and bleeding
- Heart rhythm problems
- Kidney failure
- Buildup of acid in the body fluids (metabolic acidosis)
- Fluid buildup in the lungs
- Weak or deformed muscles (myopathy or muscular dystrophy)
When to Contact a Medical Professional
If you need surgery, tell both your surgeon and anesthesiologist before surgery if:
- You know that you or a member of your family has had problems with general anesthesia
- You know you have a family history of MH
Using certain medicines can prevent the complications of MH during surgery.
Tell your health care provider before having surgery with general anesthesia, if you or anyone in your family has MH.
Avoid stimulant drugs such as cocaine, amphetamine (speed), and ecstasy. These drugs may cause problems similar to MH in people who are prone to this condition.
Genetic counseling is recommended for anyone with a family history of myopathy, muscular dystrophy, or MH.
American Association of Nurse Anesthesiology. Malignant hyperthermia crisis preparedness and treatment: position statement. 10.
Yepuri N, Pruekprasert N, Cooney RN. Surgical complications. In: Townsend CM Jr, Beauchamp RD, Evers BM, Mattox KL, eds. Sabiston Textbook of Surgery. 21st ed. St Louis, MO: Elsevier; 2022:chap 12.
Zhou J, Nozari A, Bateman B, Allen PD, Pessah IN. Neuromuscular disorders including malignant hyperthermia and other genetic disorders. In: Gropper MA, ed. Miller's Anesthesia. 9th ed. Philadelphia, PA: Elsevier; 2020:chap 35.
Last reviewed on: 6/12/2023
Reviewed by: Jacob Berman, MD, MPH, Clinical Assistant Professor of Medicine, Division of General Internal Medicine, University of Washington School of Medicine, Seattle, WA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.