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Is there a link between malignant hyperthermia and exertional heat illness?

Muldoon SM, Deuster P, Brandom BW, Bunger R. Exercise and Sport Sciences Reviews, 2004

It has been suggested that people who have experienced an episode of exertional heat illness may be more prone to malignant hyperthermia and vice versa due to a similar genetic mutation. Malignant hyperthermia (MH) is an anesthetic emergency that develops in response to certain anesthetic medications, specifically those given during general anesthesia - inhaled anesthetics and succinylcholine. MH is recognized by a constellation of findings including an increase in heart rate and blood pressure, elevated amount of acid in the body, muscle rigidity, and elevated body temperature (which is the basis of the disease’s name "malignant hyperthermia”). Serious consequences can result if the patient does not receive treatment with dantrolene, a muscle relaxant. These consequences include multi-organ failure and eventual death. MH is linked to a genetic mutation which causes the release of an excessive amount of calcium from certain parts of muscle cells. In the process of counteracting the massive calcium release, the body experiences deadly overheating. While the trigger of exertional heat illness (EHI) is different than that of MH, the end result of excessive body temperature is very similar. EHI is caused by prolonged exercise or work in hot temperatures leading to increased blood flow to muscles and less blood flow to vital organs, like the gastrointestinal system, which ultimately causes release of toxins and pro-inflammatory proteins into the body. This release of toxins and proteins causes elevated body temperature which then can lead to exertional heat stroke, a serious and life-threatening overheating that can result in multi-organ failure and death. The release of similar inflammatory proteins in both EHI and MH prompted research into a common link between MH and EHI. It was discovered through genetic testing for predisposition towards MH that a large number of people who have had one or more episodes of EHI tested positive for high susceptibility of MH. Thus, it is suggested that people with a history of EHI can be pre-disposed to having MH when undergoing anesthesia and that those with a history of MH can be predisposed to EHI. It is important for people who have a history of EHI to inform their surgeon and especially their anesthesiologist if they are planning on undergoing surgery so that proper safety precautions can be set up and alternate anesthetic medications can be used. Similarly, people with a history of MH should also be aware of their possibility of susceptibility to EHI.

~ Josephine Orrico, MD - Mount Sinai St. Luke's and Roosevelt

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