Malignant Hyperthermia Health Article

Demographics

The exact number of individuals who are born with a genetic change that causes MH susceptibility is not known. Until genetic research and genetic testing improves, this number will likely remain unclear. However, it is estimated that internationally 1 in 50,000 people who are exposed to anesthesia develop an MH reaction. Among children, it is estimated that one in 5,000 to one in 15,000 develop MH symptoms when exposed to anesthesia. MH has been seen in many countries, although there are some geographic areas where it occurs more often in the local populations, including parts of Wisconsin, North Carolina, Austria, and Quebec.

Signs and symptoms

Although the specific symptoms of malignant hyperthermia can vary, the most common findings include:

• stiffness/spasms of jaw muscles and other muscles
• rapid breathing, causing decreased oxygen and increased carbon dioxide in the blood
• rapid or irregular heartbeat
• high body temperature (over 110°F)
• muscle breakdown (may cause dark or cola-colored urine)
• internal bleeding, kidney failure, brain damage, or death (if not treated successfully)

Diagnosis

The diagnosis of MH susceptibility can be made before or during a reaction to a triggering drug. Ideally, the diagnosis is made before a susceptible individual is exposed and/or develops a reaction. This is possible for people who learn they have an increased chance for MH because hey have a relative with MH susceptibility. Testing these individuals requires a surgical procedure called a muscle biopsy, in which a piece of muscle tissue is removed from the body (usually from the thigh). Safe (i.e., non-triggering) anesthetics are used during the procedure. The muscle is taken to a laboratory and is exposed to halothane (a triggering anesthetic) and caffeine, both of which cause any muscle tissue to contract, or tighten. Thus the test is called the caffeine halothane contracture test (CHCT). Muscle tissue taken from individuals with MH susceptibility is more sensitive to caffeine and halothane, causing it to contract more strongly than normal muscle tissue from non-susceptible people. This type of test is a very accurate way to predict whether a person has MH susceptibility or not. However, the test does require surgery, time to recover (typically three days), and it is expensive (approximately $2,500). In the United States, many insurance companies will pay for the testing if it is needed. Although the test is not available in every state or country, there are at least 40 medical centers worldwide that can perform the test.

Unfortunately, not all MH susceptible people will learn from their family histories that they have an increased risk for MH before they are exposed to a trigger drug. For these individuals, the diagnosis of MH susceptibility is often made during surgery by the anesthesiologist (a physician specializing in anesthesia) who is providing the anesthesia medications. Other health care specialists also may notice symptoms of MH during or after surgery. Symptoms such as rapid breathing, rapid heart rate, and high body temperature can usually be detected with various machines or devices that examine basic body functions during surgery. Muscle stiffness of the jaw, arms, legs, stomach and chest may be noticed as well. These symptoms may happen during surgery or even several hours later. If the diagnosis is made during or after surgery, immediate treatment is needed to prevent damage to various parts of the body or death. If a person has a suspicious reaction to anesthesia, he or she may undergo a muscle biopsy to confirm MH susceptibility at a later date.

In spite of fact that a number of important genes and genetic regions associated with MH susceptibility have been identified, testing a person's DNA for all of the possible changes that may cause this condition is not easily done for affected individuals and their families. Existing genetic testing identifies some changes that have been seen among families with MHS1 and MHS6. Research studies may provide information for families with MHS2, MHS3, MHS4, and MHS5 as well. Sometimes the testing requires DNA from only one affected person, but in other cases, many samples are needed from a variety of family members. However, until genetic technology improves, the contracture test that is done on muscle tissue will likely remain the "gold standard" for diagnosis of MH susceptibility.