MH is a chain reaction event (a syndrome) "triggered" in susceptible individuals by commonly used general anesthetics. The signs of MH include a greatly increased body metabolism, muscle rigidity and eventual hyperthermia which may exceed 110 degrees F. Death can result from cardiac arrest, brain damage, internal hemorrhaging or failure of other body systems.

MH susceptibility has an autosomal dominant inheritance. This means that children and siblings of a patient with MH susceptibility have a 50% chance of inheriting the gene for MH and hence would be MH susceptible also. Those who are susceptible may be completely unaware of this risk unless they or a family member developed a life-threatening crisis during anesthesia. It is important to know that not everyone who has a gene defect linked to MH develops an MH episode upon each exposure to the triggering anesthetics. Unfortunately, the gene for this disorder has not been definitively identified.

The exact incidence of MH is unknown. The rate of occurrence has been estimated to be as frequent as one in 5,000 or as rare as one in 65,000 administrations of general anesthesia with triggering agents.

The volatile gaseous inhalation anesthetics (e.g., halothane, enflurane, isoflurane, sevoflurane and desflurane) are MH triggers, as is the depolarizing muscle relaxant succinylcholine. All other anesthetic drugs are safe. Some examples of safe anesthetics are: nitrous oxide, local anesthetics, narcotics, propofol, thiopental, curare, atracurium.

Treatment consisted only of cooling the patient and treating specific symptoms but not the underlying cause.

The best way to prevent MH is through detection of those at risk prior to surgery. Patients with a family history of MH or suggestive of MH should ensure that this information is communicated to his/her anesthesia caregiver. Patients should ensure that the facility (hospital, surgery center, office) is stocked with dantrolene in sufficient quantities for a crisis (36 vials) and that a treatment protocol is available.

Because MH is considered a dominantly inherited disorder, all members of a family in which MH has occurred must also be considered MH susceptible and managed accordingly, unless proven otherwise. It should be noted that those who have had previous anesthetics without problem cannot be certain they are not at risk - deaths have occurred even though patients have undergone multiple prior uneventful surgeries. Certainly any family with a history of anesthetic deaths or complications should make this known to the anesthesiologist before undergoing surgery.

There is currently no simple diagnostic test available for screening the general population (e.g., a blood test). The most accurate test involves a biopsy of skeletal muscle from the thigh. It is usually reserved for those with a family history of MH or when a patient has had a previous suspicious reaction to anesthesia.