Incidence of Malignant Hyperthermia in the General Population
The incidence of malignant hyperthermia (MH) in the general population is estimated to range from 1:10,000 to 1:250,000 general anesthetics, with the most recent and reliable UK data suggesting an incidence of approximately 1:100,000 to 1:250,000 anesthetics. 1
Epidemiological Considerations
The reported incidence of MH varies significantly due to several factors that affect accurate estimation:
- Reporting challenges: Incomplete reporting of suspected reactions
- Diagnostic confirmation: Failure to confirm diagnosis with definitive testing
- Denominator accuracy: Inaccurate estimates of total general anesthetics administered
- Data collection methods: Use of administrative databases with varying reliability 1
Regional Variations
In the United Kingdom:
- Approximately 20 confirmed new cases of MH occur each year
- Using Royal College of Anaesthetists' data (3 million general anesthetics annually), the incidence is approximately 1:100,000 1
- Using international data on anesthetic administration rates (1 anesthetic per 10 population annually), the UK incidence is closer to 1:250,000 1
Demographic Patterns
Important demographic patterns in MH incidence include:
- Age distribution: Higher incidence in pediatric populations
- Gender distribution: Consistently higher incidence in males compared to females
- Genetic prevalence: Genetic variants associated with MH risk have a combined prevalence of less than 1:2000 in the general population, significantly higher than the clinical incidence 1
Trends in Incidence
The number of MH cases has shown some notable trends:
- Slight decrease in annual cases over time
- Reduction correlates with decreased use of suxamethonium (a known trigger)
- Cases during inhalational anesthesia without suxamethonium have remained relatively constant over the past 40 years 1
Discrepancy Between Genetic Prevalence and Clinical Incidence
An important clinical consideration is the significant discrepancy between:
- Genetic prevalence of MH-associated variants (approximately 1:2000)
- Clinical incidence of MH reactions (1:10,000 to 1:250,000)
This suggests reduced penetrance of MH susceptibility, with both genetic and non-genetic factors likely contributing to whether a susceptible individual will experience an MH reaction when exposed to triggering agents 1
Mortality Considerations
While not directly related to incidence, it's worth noting that mortality from MH has decreased dramatically:
- Historical mortality: 70-80% in the 1960s
- Current mortality: Approximately 4% in the UK with proper treatment 1
- Early recognition and prompt treatment are critical for reducing mortality 2, 3
Clinical Implications
The relatively low incidence of MH, combined with its potentially fatal consequences, underscores the importance of:
- Maintaining vigilance during anesthesia administration
- Recognizing that prior uneventful anesthesia does not rule out MH risk
- Having dantrolene sodium available wherever general anesthesia is administered
- Early recognition of signs, particularly elevated end-tidal CO2
- Prompt discontinuation of triggering agents when MH is suspected 1