Should we reassess the susceptibility of MH patients?

Abstract

I N this issue of the Canadian Journal of Anaesthesia, Drs. Bachand and colleagues present us with a remarkable study, Clinical Reassessment of Malignant Hyperthermia in Abitibi-T~miscamingue. As a result of their extraordinary efforts, more than 1,000 individuals in Northwest Quebec will lose their malignant hyperthermia (MH) susceptible label. The percentage of individuals considered at high risk for MH susceptibility will decrease by 60% (1.2% ~ 0.47%). These important results were produced by the convergence of several factors. First, Dr. Bachand and her colleagues successfully contacted 1,546 individuals, retrieved 2,073 medical charts, and evaluated 1,597 general anaesthetic records to determine the likelihood of an MH event. Second, every MH susceptible individual asked to participate in this study, gave consent for inclusion. Third, Catholic parish registers provided investigators with four centuries of outstanding genealogical documentation so that complete ascending family trees from 20th century probands to their 17th century ancestors could be constructed. Fourth, in 1994, a panel of international MH experts developed a clinical grading scale to provide a clinical case definition for the MH syndromeJ The MH clinical grading scale uses standardized clinical criteria and does not rely on other MH laboratory diagnostic tests. The grading scale asks the anaesthetist to judge the appropriateness of various clinical signs considered in the context of the patient's anaesthetic technique, underlying medical diseases, and procedure. Only clinical signs considered inappropriate for the clinical situation are used to score the likelihood that an adverse reaction to anaesthesia is an MH event. The grading scale may underestimate the likelihood of an MH event if an anaesthetic was aborted early in the course of a reaction, if patient monitoring was incomplete (especially absent capnography) or essential laboratory studies were not performed (e.g., arterial blood gas analysis). The clinical grading scale was developed to standardize the diagnosis of MH susceptibility so that research studies such as Dr. Bachand's could be conducted. Fifth, in the past decade, the North American Malignant Hyperthermia Group and Registry standardized and validated the MH diagnostic muscle .biopsy (North American caffeine halothane contracture test) facilitating the determination of MH susceptibility in the study population.2,3, 4 Why should clinicians care about clinically reassessing individuals labelled as MH susceptible? Given the availability of dantrolene and modern intravenous anaesthetic agents, how much damage can an erroneous diagnosis of MH susceptibility cause? I believe clinicians should apply a label of MH susceptibility to a patient only after careful investigation for the following reasons. Mislabeling a patient as MH susceptible prevents the anaesthetist from using the full range of anaesthetic medications helpful in the management of patients with serious co-existing diseases. For example, potent inhalational anaesthetics are very helpful in the management of patients with status asthmaticus or epiglottitis but will be contraindicated for patients inappropriately labelled MH susceptible. Mislabeling patients leads to increased use of expensive and scarce medical resources. When a patient is considered MH susceptible, he will spend additional time in the post anaesthesia care unit and hospital prior to discharge. Additionally, patients may need to be referred to tertiary care facilities at a distance from their homes. Mislabeling families may trigger unnecessary, expensive, and invasive MH diagnostic muscle biopsies of the proband's relatives. Individuals mislabeled as MH susceptible will not have the opportunity to enroll in the military forces. Those mislabeled as MH susceptible must acquire and wear Medic-Alert bracelets or necklaces which mark MH susceptible children as different from their peers. When MH susceptible adolescents try to abandon these labelling devices, serious family discord may ensue. Finally, patients mislabeled as MH susceptible