Malignant hyperthermia

Malignant hyperthermia is a rare but life-threatening reaction to certain drugs used during general anesthesia. It happens when anesthesia drugs trigger a dangerous increase in body temperature and severe muscle contractions. This reaction occurs in people who have inherited a specific genetic mutation that affects how their muscles respond to certain medications.

The condition affects about 1 in 100,000 adults and 1 in 30,000 children who receive anesthesia. When triggered, body temperature can rise rapidly, sometimes reaching 105 degrees Fahrenheit or higher. Muscles break down quickly, releasing harmful substances into the bloodstream. Without immediate treatment, malignant hyperthermia can cause organ damage, brain injury, or death.

Most people with the genetic mutation never know they have it until they receive anesthesia. Family history is the strongest predictor of risk. The condition follows an autosomal dominant pattern, meaning you only need one copy of the mutated gene from one parent to be at risk. If you have the mutation, each of your children has a 50 percent chance of inheriting it.

Malignant hyperthermia symptoms appear during or shortly after anesthesia exposure. Common signs include:

• Rapid rise in body temperature, sometimes 1 to 2 degrees every 5 minutes
• Severe muscle rigidity, especially in the jaw
• Fast or irregular heartbeat
• Rapid breathing or increased carbon dioxide levels
• Excessive sweating
• Mottled or discolored skin
• Dark or cola-colored urine from muscle breakdown
• Dangerously high potassium levels in blood
• Acid buildup in blood, called metabolic acidosis

Without anesthesia exposure, people with the genetic mutation have no symptoms. The reaction only occurs when triggered by specific anesthetic drugs. Early recognition by medical staff is critical for survival.

Malignant hyperthermia is caused by inherited mutations in genes that control calcium release in muscle cells. The most common mutation affects the RYR1 gene, which accounts for about 70 percent of cases. Other mutations can affect the CACNA1S gene. These genetic changes cause muscle cells to release too much calcium when exposed to triggering drugs, leading to uncontrolled muscle contractions and heat production.

The main triggers are volatile anesthetic gases like sevoflurane, desflurane, and isoflurane, plus the muscle relaxant succinylcholine. Risk factors include having a family history of malignant hyperthermia, unexplained death during anesthesia in a family member, muscle diseases like central core disease, or a personal history of unexplained high fever during surgery. Stress, heat, and intense exercise do not trigger malignant hyperthermia, only specific anesthetic drugs do.

Malignant hyperthermia is primarily diagnosed through genetic testing and specialized muscle biopsy. The gold standard test is called a caffeine halothane contracture test, where a small piece of muscle tissue is exposed to triggering substances in a lab. This test requires a muscle biopsy and is only available at specialized centers. Genetic testing can identify mutations in the RYR1 and CACNA1S genes, confirming susceptibility in about 70 to 80 percent of families with the condition.

Blood tests during an acute episode show signs of muscle breakdown, including elevated creatine kinase, high potassium, and myoglobin in urine. Some people may have allergy testing for anesthetic drugs like succinylcholine, which can show IgE antibodies. However, drug allergy tests do not diagnose malignant hyperthermia susceptibility itself. Talk to a doctor about specialized genetic testing if you have a family history of anesthesia complications.

Treatment for malignant hyperthermia requires immediate medical intervention. Key approaches include:

• Stop all triggering anesthetic drugs immediately
• Give dantrolene, the only specific treatment that stops the reaction
• Cool the body with ice packs, cold intravenous fluids, and cooling blankets
• Provide 100 percent oxygen to support breathing
• Monitor and correct dangerous electrolyte imbalances, especially high potassium
• Support kidney function to prevent damage from muscle breakdown products
• Continue dantrolene for 24 to 48 hours to prevent recurrence
• Monitor in intensive care for at least 24 hours after stabilization

If you are diagnosed with malignant hyperthermia susceptibility, you need special precautions for any future surgeries. Always inform surgeons and anesthesiologists about your condition. Wear a medical alert bracelet or necklace. Safe anesthesia options exist, including propofol and other non-triggering drugs. Family members should consider genetic testing or muscle biopsy to determine their risk.