Summary about Disease
Malignant hyperthermia (MH) is a rare, life-threatening inherited disorder triggered by certain anesthetic agents and, in rare cases, by strenuous exercise in susceptible individuals. It causes a rapid and severe increase in body temperature and muscle rigidity, along with other metabolic abnormalities. It is a pharmacogenetic disorder, meaning it's caused by a genetic predisposition that affects how the body responds to certain drugs.
Symptoms
Symptoms of MH can develop rapidly, often during or shortly after anesthesia. Key symptoms include:
Muscle rigidity, especially of the jaw (masseter spasm)
Rapid heart rate (tachycardia)
Rapid breathing (tachypnea)
Increased body temperature (hyperthermia), often a late sign
Increased carbon dioxide production
Sweating
Mottled skin
Muscle breakdown (rhabdomyolysis), leading to dark urine
Cardiac arrhythmias
Increased acid levels in the blood (acidosis)
Causes
MH is caused by genetic mutations in genes that control calcium release in muscle cells, most commonly the RYR1 gene. These mutations lead to an uncontrolled release of calcium in the muscle cells when triggered by certain anesthetic agents (volatile anesthetics like sevoflurane, isoflurane, desflurane, and the muscle relaxant succinylcholine). Rarely, strenuous exercise can also trigger MH in susceptible individuals. It's an inherited condition, meaning it's passed down through families.
Medicine Used
The primary medication used to treat MH is dantrolene. Dantrolene is a muscle relaxant that acts directly on skeletal muscle to inhibit calcium release from the sarcoplasmic reticulum, thus reversing the uncontrolled muscle contraction and associated metabolic abnormalities. Other supportive treatments include:
Oxygen
Cooling measures (ice packs, cooling blankets, iced saline infusions)
Treatment of cardiac arrhythmias
Correction of electrolyte imbalances and acidosis
Management of rhabdomyolysis
Is Communicable
No, malignant hyperthermia is not communicable or contagious. It is a genetic disorder that is inherited, not an infectious disease.
Precautions
For individuals known to be susceptible to MH or with a family history of MH, the following precautions are essential:
Inform all medical professionals (anesthesiologists, surgeons, dentists) about the susceptibility or family history before any procedure requiring anesthesia.
Avoid triggering anesthetic agents (volatile anesthetics and succinylcholine).
Use alternative anesthetic techniques, such as total intravenous anesthesia (TIVA) with agents like propofol and opioids.
Ensure the operating room is "MH-ready" with dantrolene available.
Genetic testing and muscle biopsy (caffeine halothane contracture test, CHCT) can help determine susceptibility.
Wear a medical alert bracelet or carry a card indicating MH susceptibility.
How long does an outbreak last?
MH is not an outbreak in the typical sense of an infectious disease. An MH episode occurs acutely, during or shortly after exposure to triggering agents. If untreated, it can be fatal. With prompt recognition and treatment with dantrolene and supportive measures, the acute crisis can be resolved within hours. The duration of symptoms depends on the severity of the reaction and how quickly treatment is initiated.
How is it diagnosed?
Diagnosis of MH is typically based on:
Clinical signs and symptoms during or after anesthesia.
Elevated end-tidal carbon dioxide (ETCO2) levels.
Tachycardia, tachypnea, muscle rigidity, and hyperthermia.
Acidosis, elevated creatine kinase (CK) levels, and myoglobinuria.
The Malignant Hyperthermia Association of the United States (MHAUS) clinical grading scale. Confirmatory testing includes:
Caffeine Halothane Contracture Test (CHCT): A muscle biopsy test that assesses the muscle's contracture response to caffeine and halothane. This is the gold standard diagnostic test.
Genetic testing: To identify specific gene mutations associated with MH susceptibility. However, a negative genetic test does not rule out MH susceptibility.
Timeline of Symptoms
The timeline of symptoms can vary, but typically follows this pattern:
Early (within minutes of exposure to triggering agents): Increased end-tidal CO2, tachycardia, tachypnea, masseter spasm.
Progressive (over minutes to hours): Generalized muscle rigidity, increased body temperature, sweating, mottled skin, cardiac arrhythmias.
Late (hours if untreated): Rhabdomyolysis, dark urine, acidosis, organ damage, cardiac arrest, death.
Important Considerations
Family History: A positive family history of MH is a significant risk factor.
Masseter Spasm: Unexplained masseter spasm after succinylcholine administration should always be considered a potential sign of MH.
Early Recognition: Prompt recognition and treatment are crucial for survival.
Dantrolene Availability: Ensure dantrolene is readily available in any setting where triggering anesthetic agents are used.
Continuous Monitoring: Vigilant monitoring of vital signs and end-tidal CO2 is essential during and after anesthesia.
Genetic Counseling: Genetic counseling is recommended for individuals with MH susceptibility or a family history of MH to assess inheritance risks.