[Incidence of disposition for malignant hyperthermia in patients with neuromuscular diseases]

It has been suggested that malignant hyperthermia (MH) occurs more frequent in patients with neuromuscular diseases (NMD) than in patients without NMD when they are exposed to volatile anaesthetics and/or succinylcholine. However, whereas central core disease (CCD) and MH susceptibility (MHS) are closely associated, the relationship between MH and other NMD is still uncertain. The purpose of this study was to evaluate the MH status of individuals with specific NMD with the in vitro contracture test (IVCT) and to ascertain the risk for MH in individuals with NMD.

After institutional approval and informed consent, 29 patients of 3-59 years of age (27.2 +/- 17.3) with clinical suspicion for NMD and MH were enrolled in this prospective study. After excision of a skeletal muscle sample from M. vastus lateralis, patients were first classified as MHS, MH-equivocal (MHE) and MH-normal (MHN) by the IVCT according to the European MH protocol. Additionally, small muscle samples were excised from each patient for histological, histochemical and morphometric examination.

Fourteen patients were diagnosed by the IVCT as MHS and 9 as MHN. In 6 patients MH status was equivocal. In six patients CCD was diagnosed, in 14 individuals muscular dystrophies and in 5 patients myotonias. Two patients had unspecific myopathies and one patient a carnitine deficiency syndrome. One patient with Friedreich's ataxia was investigated because of a MH crisis and classified as MHE. All CCD patients and two of three individuals with Duchenne's muscular dystrophy were tested as MHS.

In this study 69% of the NMD patients were diagnosed as susceptible to MH with the IVCT. These results suggest, that NMD patients bear a high risk for MH. On the other hand, it has been discussed that in vitro contracture testing is not specific in NMD patients because skeletal muscle specimens from these patients have an elevated in vitro sensitivity. However, regarding our results and from a clinical point of view, patients with NMD should be treated like MHS individuals, unless they have undergone IVCT and were classified as MH-normal.