Formal diagnosis of Malignant Hyperthermia (MH) is important to enable safe and trigger free anaesthetics in patients who are MH susceptible. 😎✅
There are two methods for testing MH susceptibility - genetic testing and muscle biopsy (also known as “in vitro contracture test”).
MH genetic testing is performed when:
1️⃣ There is a known familial genetic variant causing MH susceptibility.
2️⃣ MH episode is suspected and/or positive following muscle biopsy.
👉 The genes investigated are those responsible for calcium movement in skeletal muscle (RYR1 and CACNAS).
👉 There are more than 300 known variants of the RYR1 gene, and more than 30 of these are known to produce MH susceptibility
👉 RYR1 gene variants are responsible for more than 99% of MH susceptibility.
👉 There is a 50% chance of MH susceptibility if a parent is susceptible.
Muscle biopsy (In vitro contracture test). 💪
Muscle biopsy is performed when:
1️⃣ MH episode suspected without a family history - de novo variant.
2️⃣ Cases where the de novo variant is unable to have genetic testing or genetic variant is unknown.
👉 A muscle biopsy is the only definitive test for MH susceptibility
👉 Muscle biopsy testing measures if there is contracture of excised muscle when exposed to caffeine and halothane.
👉 Susceptibility is determined by contracture presence and magnitude.
👉 There are currently only three MH testing centres in Australia.
It is important to note that for patients with a family history of MH, a muscle biopsy may be required to confirm diagnosis - if genetic testing is negative, these patients would still be considered at risk of MH until muscle biopsy has been performed, as susceptibility can not be ruled out without muscle biopsy.
Be sure to check out our Advanced Anaesthesia Live Series on Malignant Hyperthermia tonight where we are joined by Dr Phillip Nelson, head of the Malignant Hyperthermia Investigation Unit at the Royal Perth Hospital!
Ref: https://www.ncbi.nlm.nih.gov/books/NBK1146/pdf/Bookshelf_NBK1146.pdf
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