Malignant Hyperthermia (MH)

A Severe Anesthetic Reaction Everyone Should Know About

In early March 2026, a widely discussed case involved a 37-year-old businessman who underwent rhinoplasty and chin contouring at a clinic in Pathumwan, Bangkok. Following general anesthesia, he failed to regain consciousness for four days and required ICU admission, with medical expenses exceeding 2 million THB. The medical team diagnosed Malignant Hyperthermia (MH)—not a surgical error, but a rare and unpredictable genetic reaction.

What is Malignant Hyperthermia (MH)?

MH is a life-threatening emergency that occurs in genetically susceptible individuals exposed to certain anesthetic agents, particularly volatile inhalation anesthetics or specific muscle relaxants.

This reaction causes uncontrolled calcium release in muscle cells, leading to:

• Severe muscle rigidity

• Rapid rise in body temperature (above 40°C)

• Cardiac arrhythmias

• Metabolic acidosis

• Muscle breakdown (rhabdomyolysis)

If not treated promptly, MH can be fatal.

The incidence is approximately:

• 1 in 100,000 anesthetic cases in adults globally

• 1 in 200,000 cases reported in Thailand

Genetic Cause

MH is inherited in an autosomal dominant pattern.
If one parent carries the mutation, each child has a 50% chance of inheriting it.

Key associated genes include:

• RYR1 (≈60% of cases)

• CACNA1S (≈1%)

• STAC3 (rare)

These genes are involved in calcium regulation within muscle cells.

Important Considerations

• Individuals with MH susceptibility may have undergone anesthesia previously without complications.

• This does not guarantee safety in future exposures, due to incomplete penetrance.

• Some cases arise from new (de novo) mutations, even without family history.

Screening and Diagnosis

There are currently two main screening methods:

1. Genetic Testing

• Blood test analyzing genes such as RYR1, CACNA1S, and STAC3

• Non-invasive

• Limitation: A negative result does not completely exclude risk

2. In Vitro Contracture Test (IVCT)

• Gold standard diagnostic test

• Requires a muscle biopsy

• Highly accurate but limited availability in Thailand

About the “14 High-Risk Surnames” in the News

The list refers only to surnames previously associated with reported cases in Thailand.
It does not mean all individuals with those surnames are at risk, nor does absence from the list guarantee safety.

Stigmatization or discrimination based on surnames should be avoided.

Role of a Genetic Counselor

A Genetic Counselor can assist with:

• Risk assessment based on family history

• Explaining benefits and limitations of genetic testing

• Interpreting test results

• Planning cascade testing for family members

• Providing psychological support

• Coordinating with anesthesiologists for safe anesthesia planning

What You Should Do Before Surgery

☐ Ask family members about any history of complications or death during anesthesia

☐ Check for family history of heat-related muscle breakdown during exercise

☐ Inform your anesthesiologist if any suspicious history is identified

☐ Carry an MH Alert Card if you are known to be at risk

☐ Consult a Genetic Counselor for further guidance

Key Takeaway

Although MH is rare, it is potentially fatal.
The most important preventive measure is awareness of family history.

Even if you are at risk, surgery can still be performed safely using non-triggering anesthetic agents.

Knowledge is the best protection.

References

• Malignant Hyperthermia Association of the United States (MHAUS): www.mhaus.org

• Asian Malignant Hyperthermia Alliance: www.amha.asia

• GeneReviews – MH Susceptibility: www.ncbi.nlm.nih.gov/books/NBK1146

Acknowledgement

With appreciation to:
Dr. Ronnaporn Weerachantachart
Preventive Medicine / Health Promotion Center Physicia