Heat, extreme exercise or febrile illness may also trigger MH

Malignant hyperthermia (MH) is a potentially life-threatening inherited disorder of muscle. Patients who are at risk for MH usually have no outward signs of muscle problems. However, when exposed to certain commonly used general anesthetics they may develop very high body temperature, increased heart rate and muscle breakdown. If not recognized and treated promptly MH may be fatal.

Approximately 800 cases of anesthetic-induced MH occur in the US each year. The mortality from anesthesia induced MH is very low. However, the potential for an MH episode to be triggered in humans by other factors, such as heat, extreme exercise or febrile illness as has been demonstrated in certain breeds of swine, has long been debated. Now, a team of researchers from the Universities of Rochester (NY), Pittsburgh (PA), the Uniformed Services University and the National Institutes of Health (Bethesda, MD) provide convincing evidence that this phenomenon can occur in humans.

Fatal Cases of Awake MH
In an article published in the journal Anesthesiology (115(5):938-945, November 2011), Groom and coauthors report two fatal cases of 'awake' MH induced by heat stress in children and refer to a third similar case. Not only do the investigators carefully document the MH-like signs and symptoms in these children, they also examine the DNA changes and test the effect of these changes on cellular physiology. Results from this study support the linkage of the DNA changes with these 'awake' MH episodes.

Better Patient Care
Genetic or DNA changes most commonly associated with susceptibility to MH are found within the gene called the ryanodine receptor (RYR1). This gene encodes a protein that regulates calcium movement within the muscle cell, which is crucial for regulating muscle contraction and metabolism. Understanding the relationship between RYR1 gene changes and the risk for MH-susceptibility has been the subject of research for many years. There are hundreds of DNA changes in this very large gene and some are clearly causal for MH. Furthermore, additional factors such as the patient's age, presence of more than one DNA change, an existing medical condition, or the addition of an environmental stressor (eg. exercise, heat stress, or febrile illness) may affect the likelihood that a life-threatening MH episode will occur. As noted by lead researcher, Robert T. Dirksen, PhD (University of Rochester), "Understanding the mechanisms behind anesthetic and non-anesthetic induced MH will lead us to potential treatments and better patient care."

More Research Needed To Identify Those At Risk
Dr. Henry Rosenberg, President of MHAUS points out that instances of fatal awake MH are very rare. "Much more research similar to the type reported in this study is needed to identify those at risk for "awake "MH and to determine how best to manage those who are MH susceptible both inside and outside the operating room" according to Dr. Rosenberg.

What Are The Implications?
What are the implications of this research? Are MH-susceptible individuals, especially children, at particular risk for heat-induced MH episodes? Until more data is available, it is difficult to advise MH-susceptible individuals about the avoidance of vigorous exercise and/or extremely hot environments. MHAUS hopes that reports such as these will serve to increase awareness about and readiness for such MH episodes, both in MH susceptible families and medical professionals. If an individual develops high body temperature and muscle rigidity, experts recommend the individual be cooled as soon as possible and brought to the nearest hospital where treatment with the treatment drug, dantrolene sodium for injection, can be initiated. A genetic test is available to identify some patients at risk for MH. At present it is not useful as a screening test.

Source: MHAUS