Malignant hyperthermia at The Children's Hospital Westmead
Appointments: (02) 9845 2367
The gene defect thought to cause malignant hyperthermia is present in about one in 5,000 to 10,000 of the population. An affected person will only be aware that they may carry this gene defect if they, or a family member, has suffered an adverse response under general anaesthesia. Most patients using this service will have a letter from their anaesthetist or local doctor outlining their abnormal response. Some of the muscle disorders, such as the muscular dystrophies or exercise-induced muscle breakdown (rhabdomyolysis), are also associated with this condition.
The testing available for malignant hyperthermia is not suitable as a general screening test for people without a history of this condition who are about to undergo anaesthesia and surgery.
The clinic assesses the suitability for diagnostic testing for malignant hyperthermia and for the provision of advice and information. Ideally families should be assessed in the MH clinic prior to testing as a detailed assessment of an adverse anaesthetic event or family tree will be needed. The clinic is an ideal setting for families to have their questions answered and receive information regarding this disease. Where it is inconvenient to attend the clinic, most of the information necessary to answer queries prior to diagnostic testing can be obtained by a telephone conversation. The average clinic appointment will take between 45 and 90 minutes.
Muscle Biopsy or in-vitro contracture test (IVCT)
The IVCT is the only diagnostic test available for the majority of people. The muscle biopsy is conducted as a day stay procedure at either The Children's Hospital at Westmead or the Ambulatory Surgical Unit within Westmead Hospital. The biopsy is usually taken from the inside of the thigh just above the knee. Four to six strips of muscle approximately 15 to 20mm long and 2 to 3 mm square are needed. This biopsy has to be taken with extreme care so to preserve the muscle structure and function. These strips are then taken to the laboratory, located in The Children's Hospital at Westmead, where they are mounted in tissue baths and exposed to known concentrations of four different chemicals. According to the response of these strips, a diagnosis of malignant hyperthermia susceptible (MHS) or malignant hyperthermia normal (MHN) may be made. The IVCT takes two to three hours to complete. Pieces of muscle are also sent to pathology for detailed examination to exclude any underlying muscle disease that may not be clinically obvious. Because of the moderate amount of muscle needed for the IVCT, children under the age of ten years are usually not suitable for testing. A recovery time of several days is needed to return to light duties and up to several months for intense physical activity.
This facility adheres to the European Malignant Hyperthermia Group Protocol for the IVCT.
Genetic Mutation Analysis — GMA
An individual's genetic code or DNA is extracted from a blood sample that is then frozen and stored. Using highly specialised techniques, known errors in the DNA may be investigated. This service is experimental at present, being part of a research project conducted by Dr Margaret Perry in association with Prof John Christodoulou. At present, GMA is limited to the investigation of malignant hyperthermia in those families where one of the known mutations has already been found.