Malignant Hyperthermia in Sweden: Clinical Presentations and Genetic Findings.

Abstract

Malignant hyperthermia (MH) is a pharmacogenetic, hypermetabolic and potentially lethal reaction to potent volatile anaesthetics and the muscle relaxant succinylcholine. To improve the understanding of MH, the aim of this retrospective study was to describe the Swedish cohort with respect to clinical manifestations, demographics and genetic findings. The Swedish MH Registry covers a total of 2852 individuals belonging to 544 different families investigated for MH since 1980. For this study, the index case in each family was included for further description. In total, MH was confirmed in 1555 individuals. Among the 288 index cases with a history of an MH reaction and confirmed MH, 58% were male and 57% were < 18 years of age. MH was confirmed in 41% of index cases where masseter muscle spasm was the only clinical sign of MH. The overall case fatality following an MH reaction in Sweden was 5.2%, but no fatal MH reaction has been reported since 2001. Out of 163 genetically investigated MH families, 61 had a diagnostic variant and 23 had a variant of unknown significance. We found that MH reactions predominantly occur in young individuals and that case fatality has declined over recent decades, with no deaths reported in the past 20 years. Less than 40% of the genetically investigated MH families, corresponding to around 20% of all Swedish MH families, currently have an identified genetic diagnostic variant. This analysis of the national Swedish Malignant Hyperthermia patient registry presents case factors and outcomes from cases among recognised families from the last 45 years. Presenting symptoms and then case confirmation details are presented, along with results from cases and families where genetic variants has been assessed.