Medically reviewed by Eland Siddle, PharmD · Last updated July 2026
Malignant hyperthermia (MH) is a rare but serious reaction to certain types of general anesthesia. It's not a disease someone lives with day to day. It's a crisis that can occur in the operating room when a susceptible person is exposed to specific anesthetic agents. With the right preparation, it is manageable.
Understanding what malignant hyperthermia is, who is at risk, and how to communicate that risk to a surgical team can make a significant difference in surgical outcomes.
What Triggers Malignant Hyperthermia?
MH is triggered by exposure to certain volatile anesthetic gases, such as halothane, sevoflurane, and desflurane, or the muscle relaxant succinylcholine, sometimes used during intubation. In a susceptible person, these agents cause an uncontrolled release of calcium inside muscle cells, leading to a cascade of dangerous symptoms.
MH is not triggered by intravenous anesthetics (such as propofol) or regional anesthesia (such as epidurals or nerve blocks). This distinction matters when planning surgery: MH-susceptible patients can safely undergo many procedures with the right anesthetic approach.
Signs and Symptoms
MH develops rapidly. Key warning signs include:
- Rapid, severe rise in body temperature (temperatures can climb to dangerously high levels very quickly)
- Muscle rigidity, especially jaw stiffness (masseter rigidity) early in the episode
- Elevated heart rate and irregular heartbeat
- Increased carbon dioxide production detected on anesthesia monitoring equipment
- Metabolic acidosis, a change in blood chemistry that signals the muscles are in crisis
MH is a medical emergency. Modern anesthesia monitoring is designed to detect these changes early, and most operating rooms are equipped to respond immediately.
Treatment: Dantrolene
The primary treatment for an active MH episode is dantrolene, a medication that works by blocking the abnormal calcium release in muscle cells. Dantrolene dramatically improved MH survival rates after it became widely available, and anesthesia teams are trained to administer it without delay when MH is suspected. Hospitals and surgical centers that perform general anesthesia are required to stock dantrolene on site.
Who Is at Risk? The Genetic Connection
MH susceptibility is largely inherited. It follows an autosomal dominant pattern, meaning one copy of a pathogenic variant (inherited from one parent) is enough to confer susceptibility. Because of this inheritance pattern, MH susceptibility tends to run through families.
The gene most commonly involved is RYR1 (ryanodine receptor 1), which encodes a protein that regulates calcium release in muscle cells. Variants in RYR1 account for the majority of identified MH susceptibility cases. Variants in CACNA1S, a related gene, account for a smaller portion.
It's worth noting that someone can carry a susceptibility variant and have had previous surgeries without incident. MH does not occur every time a susceptible person receives an anesthetic trigger, which is precisely why genetic knowledge is valuable.
MH Susceptibility: What the Surgical Team Needs to Know
| If you have known MH susceptibility | If MH susceptibility is unknown |
|---|---|
| Inform your anesthesiologist and surgical team before every procedure involving general anesthesia | A family history of anesthesia complications or unexplained deaths during surgery should prompt a conversation with your doctor |
| Request that volatile anesthetic agents and succinylcholine be avoided; total intravenous anesthesia (TIVA) is often used instead | Genetic testing can identify RYR1 and CACNA1S variants before any surgical situation arises |
| Confirm the surgical facility stocks dantrolene | Discuss family history with a genetic counselor if relatives have had unexplained anesthesia reactions |
| Carry documentation (such as a medical alert card) noting MH susceptibility | Standard preoperative screening does not routinely test for MH susceptibility |
The Malignant Hyperthermia Association of the United States (MHAUS) is a reliable resource for patients and families seeking more information on MH protocols and how to communicate susceptibility to care teams.
Why Early Identification Matters
MH susceptibility causes no symptoms outside of an anesthetic exposure. A child or adult with a RYR1 variant can be entirely healthy with no idea the variant exists, until they undergo surgery. This is what makes proactive identification meaningful. Knowing in advance gives a family and their medical team time to plan, choose appropriate anesthetics, and approach surgery with confidence rather than uncertainty.
If you're interested in learning more about how genetic testing can identify MH susceptibility, see our related article: Can Genetic Testing Detect Malignant Hyperthermia Risk?
Where Fore Fits
Fore's pediatric genetic screen uses whole genome sequencing (WGS), the most comprehensive form of genetic testing available, to screen for more than 1,000 genetic conditions, including variants associated with MH susceptibility in genes like RYR1 and CACNA1S. Every screen includes board-certified genetic counseling to help families understand results and next steps.
The screen is done at home with a cheek swab, no clinic visit required. The lab is CLIA-certified and CAP-accredited, and results are protected under HIPAA. Fore also provides lifetime reanalysis, so as science advances, your child's data is reinterpreted against new findings.
If you'd like to learn more about what whole genome sequencing involves, our article What Is Whole Genome Sequencing? is a good starting point. And if you're wondering what a genetic counselor actually does with your results, What Does a Genetic Counselor Do? walks through the process.
Learning about a potential susceptibility now, before any surgical situation arises, is exactly the kind of proactive step families take when they want to be prepared. Learn more about the Fore screen.
Personalized Care, Not Prediction
Knowing about a condition like malignant hyperthermia matters most in the moments before a medical procedure. Traditional medicine tends to ask: is my child sick? Fore is built around a different question: how do we help keep them healthy? That shift matters, because a genetic finding is not a diagnosis.
- A variant is not a verdict. Most children who carry one will never develop the associated condition.
- It points to personalized care, not a fixed fate. A finding identifies who may benefit from closer attention, not who is destined to get sick.
- It gives your pediatrician a head start. Depending on the finding, that can mean earlier eye or hearing exams, periodic heart monitoring, earlier cholesterol screening, avoiding a specific medication, or simply noting the result to watch over time.
- The goal isn't predicting the future. It's making your child's care more personalized from day one.
Fore's at-home whole genome screen covers 1,000+ conditions and 100+ medication responses, includes board-certified genetic counseling, and reanalyzes your child's genome over time as science advances. See what Fore screens for.
FAQs
Is malignant hyperthermia the same as a fever or heat stroke?
No. Malignant hyperthermia is a specific pharmacogenetic reaction triggered by certain anesthetic agents in the operating room. It is not caused by environmental heat or illness. The rapid temperature rise in MH comes from uncontrolled muscle metabolism, not from an external heat source or infection.
Can someone with MH susceptibility safely have surgery?
Yes. Knowing about MH susceptibility in advance allows the anesthesia team to avoid the triggering agents entirely. Total intravenous anesthesia (TIVA), which does not involve volatile gases, is a well-established alternative. With proper planning, surgery is safe for MH-susceptible patients.
How is MH susceptibility inherited?
MH susceptibility follows an autosomal dominant inheritance pattern. This means one pathogenic variant in a relevant gene, most often RYR1, is enough to confer susceptibility. A parent who carries such a variant has a 50% chance of passing it to each child.
If a family member had an MH reaction, should other relatives be tested?
A family history of MH reactions is a strong reason to discuss genetic testing with a physician or genetic counselor. Because MH susceptibility is inherited, biological relatives of an affected person may carry the same variant. A genetic counselor can help determine which testing approach makes sense for your family.
Does genetic testing for MH require a blood draw or clinic visit?
Not necessarily. Some genetic tests, including Fore's at-home pediatric screen, use a cheek swab collected at home. However, the appropriate type of testing depends on clinical context. Speak with a physician or genetic counselor about what is right for your situation.