17945 Malignant Hyperthermia

Overview

Malignant hyperthermia is a rare, inherited condition that can cause a severe reaction to certain medicines used to put people to sleep during surgery (general anesthetics). When a person with this condition receives those medicines, their body temperature can rise dangerously high and their muscles can become very stiff. It needs urgent medical treatment.

Malignant hyperthermia is very rare. It is estimated to occur in about 1 in 5,000 to 1 in 50,000 surgeries where general anesthesia is used.

People of any age can have malignant hyperthermia, but it is most commonly noticed in children and young adults. It affects both males and females, though some studies suggest it may be slightly more common in males. Many people with the genetic change do not know they have it until they have anesthesia.

Symptoms

Common symptoms

• A sudden, very high body temperature (often above 40°C / 104°F) during or after anesthesia
• Severe muscle rigidity or spasms, especially in the jaw and chest
• Rapid or irregular heartbeat
• Fast, deep breathing or difficulty breathing
• Dark brown or cola-colored urine (a sign of muscle breakdown)
• Excessive sweating
• Muscle pain or tenderness in the days after surgery

Symptoms in children

• High fever that spikes quickly
• Severe muscle stiffness, especially after starting anesthesia
• A very fast heart rate
• Signs of distress, such as floppiness or unusual stillness in infants
• Dark urine

Symptoms in older adults

• Fever may be less noticeable, so closer monitoring is needed during and after surgery
• Muscle rigidity may be mistaken for other conditions, such as neurological issues
• Older adults may have heart rhythm changes that require immediate attention

Causes

Main causes

• A genetic change (mutation) that affects how muscle cells handle calcium, causing muscles to overreact to certain anesthetic medicines.
• The trigger is exposure to specific inhaled anesthetics (such as halothane or sevoflurane) and a certain muscle relaxant (succinylcholine) used to help with breathing tubes.
• Without the trigger, a person with the gene change typically has no symptoms.

Risk factors

• Having a blood relative who has malignant hyperthermia or a known family history of the condition
• Having certain inherited muscle disorders, which can increase the chance of a reaction
• A past episode of malignant hyperthermia during anesthesia
• Being of any age, though children and young adults are more commonly affected

When to see a doctor

See a doctor urgently if:

• If you or a family member develops symptoms like high fever, muscle stiffness, or very dark urine during or right after anesthesia, call your local emergency number immediately.
• If you know you carry the malignant hyperthermia gene and need to have any surgery, tell your healthcare team right away so they can plan safe anesthesia.

Book a routine appointment if:

• If you have a family history of malignant hyperthermia, talk to your doctor before any planned surgery or procedure that requires general anesthesia.
• If you experienced unexplained muscle pain, fever, or dark urine after a past surgery, discuss this with your doctor to see if testing is needed.

Diagnosis

Malignant hyperthermia is usually diagnosed during surgery when a person shows the typical signs, such as a rapid rise in temperature and severe muscle rigidity. After the person is stable, doctors may recommend genetic testing or a muscle biopsy to confirm the diagnosis and determine if family members are at risk.

Tests that may be done

• A blood test to check for elevated creatine kinase (CK), a muscle enzyme that increases when muscles break down.
• Genetic testing to look for mutations in the RYR1 gene, the most common cause of malignant hyperthermia.
• A muscle contracture test (also called the caffeine-halothane contracture test) — a highly sensitive test that involves a small sample of muscle tissue being exposed to triggering substances to see how it reacts. This test is only done at specialized centers.

What to expect at your appointment

If malignant hyperthermia is suspected during surgery, the anesthetic is stopped and immediate treatment begins. This is not a time for tests — treatment comes first. After the emergency is under control, you and your family will be referred to a specialist, usually a neurologist or genetic counselor, to discuss follow-up testing and what it means for you and your relatives.

Treatment

Malignant hyperthermia is a medical emergency. Treatment starts immediately by stopping the triggering anesthetics, giving a specific reversal medicine (called dantrolene) to calm the muscles, and cooling the body down. Other measures may include IV fluids, oxygen, and correcting blood chemistry imbalances.

Self-care at home

• There is no self-care for an acute episode — call emergency services right away if you suspect it.
• Before any surgery, always tell your healthcare team that you have or may have malignant hyperthermia.
• Wear a medical alert bracelet or carry a card that says you are at risk for malignant hyperthermia.

Medical treatments

The main treatment is a specific medication that relaxes muscles and stops the overreaction. Doctors will also take steps to lower your body temperature, give oxygen, and provide fluids and medicines to protect your kidneys and heart. Everyone who is at risk should be treated in a hospital with the necessary antidote available. You will need to stay in the hospital for observation for at least 24 hours after an episode.

When is surgery considered?

If you are known to be at risk, you can safely have surgery. The anesthesiologist will avoid the triggering anesthetics and use what are called 'trigger-free' anesthetics instead. These medicines are safe for people with malignant hyperthermia. Your care team will also have the antidote and cooling equipment ready in the operating room. It is important to arrive at the hospital with a clear written plan about your condition.

Living with this condition

Most people with malignant hyperthermia live completely normally with no symptoms day to day. The only important thing is to avoid the triggers. This means telling every new doctor, anesthesiologist, or healthcare provider about your condition before any surgery, procedure, or even dental work that might involve anesthesia.

Lifestyle tips

• Wear a medical alert identification bracelet or necklace that lists your risk for malignant hyperthermia.
• Carry a wallet card with details about your condition and your genetics test results if you have them.
• Talk to your family members — because it is inherited, your blood relatives may also be at risk. Encourage them to discuss testing with their doctor.
• Before any scheduled surgery, double-check with the anesthesia team that they have a safe plan for you.

Diet and exercise

There are no specific dietary restrictions or exercise limitations for people with malignant hyperthermia. You can eat a normal, balanced diet and exercise as you normally would. If you ever experience muscle pain, dark urine, or weakness after exercise, seek medical advice promptly, but this is not common.

Mental health and emotional wellbeing

Learning that you have a rare condition that could be triggered during surgery can feel worrying. It may also cause guilt if you pass the gene to your children. These feelings are normal. It can help to talk to a counselor or genetic counselor who can explain the facts and ease your fears. If you ever feel overwhelmed, anxious, or depressed, please reach out to a mental health professional or a crisis support line in your area.

Prevention

You cannot change the gene, but you can prevent dangerous episodes by avoiding the triggering anesthetics. If you are at known risk, your anesthesiologist can use safe alternatives and take special precautions so you can have surgery without harm. Prevention also includes telling all healthcare providers about your condition before any procedure.

Vaccines

There is no vaccine to prevent malignant hyperthermia.

Screening programmes

Family screening is important. If one person is diagnosed with malignant hyperthermia, their close blood relatives (parents, children, siblings) should consider genetic counseling and testing. Testing can tell you whether you carry the gene change so you can take precautions before any future surgery.

Complications

If left untreated

• Extremely high body temperature leading to damage to the brain and other organs
• Breakdown of muscle tissue, which can release large amounts of protein into the blood and cause acute kidney injury
• Life-threatening heart rhythm problems
• Swelling of the muscles that can lead to compartment syndrome
• Without prompt treatment, the condition can be fatal

Long-term outlook

With rapid recognition and proper treatment, the vast majority of people who experience malignant hyperthermia recover completely. The key is having the right medicines and equipment available in the operating room — which is standard in modern hospitals. Once you know you are at risk, you can undergo future surgeries safely with careful planning. There is every reason to live a full, active, and healthy life.

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