Effects of the phosphodiesterase-III inhibitor enoximone on skeletal muscle specimens from malignant hyperthermia susceptible patients

STUDY OBJECTIVES

To study the in vitro effects of the phosphodiesterase-III inhibitor enoximone on skeletal muscle specimens from malignant hyperthermia susceptible (MHS) and normal (MHN) patients.

DESIGN

Prospective study.

SETTING

Malignant hyperthermia (MH) laboratory at a university hospital.

PATIENTS

47 patients with clinical suspicion for MH undergoing in vitro contracture test (IVCT) for diagnosis of MH susceptibility.

INTERVENTIONS

Biopsies of M. quadriceps femoris were performed in adult patients with a 3-in-1 nerve block and in children with trigger-free general anesthesia.

MEASUREMENTS AND MAIN RESULT

Patients were first classified as MHS or MHN by the IVCT according to the protocol of the European MH Group (EMHG). Patients with equivocal results (MHE) or with neuromuscular diseases were excluded from the study. Enoximone was added to the organ bath to surplus vital muscle specimens in single bolus concentrations of 0.4, 0.6, 0. 8, or 1.6 mmol/L. The in vitro effects of enoximone on muscle contractures and twitch were measured. Seventeen patients were classified as MHS and 30 as MHN by the EMHG criteria. Enoximone induced contractures in skeletal muscles in a dose-dependent manner. Contractures of MHS compared to MHN muscle specimens were significantly larger at all concentrations used in this study. No overlap in maximum contractures was seen between MHS and MHN muscles at a bath concentration of 0.6 mmol/L enoximone only.

CONCLUSIONS

Diagnosis of MH by an IVCT test with a single bolus administration of enoximone seems to be possible using a concentration of 0.6 mmol/L. The findings of this study may indicate an involvement of the phosphodiesterase-III and cAMP system in pathogenesis of MH. Further in vivo investigation should determine the trigger potency of enoximone in MH susceptible individuals.

Classification of malignant hyperthermia-equivocal patients by 4-chloro-M-cresol

To clarify the contracture response to 4-chloro-m-cresol (4-CmC) in malignant hyperthermia (MH) equivocal (MHE) muscle, we studied the effect of cumulative concentrations of 4-CmC. In vitro contracture test (IVCT) was performed in 35 probands according to the European MH test protocol. Surplus muscle bundles were exposed to 4-CmC (25-200 micromol/L), maintaining each concentration for 4 and 8 min. After 4 min exposure, the contracture increase of MH susceptible (MHS) (n = 7) muscle specimens was significantly (P = 0.05) greater at 50 micromol/L compared with either MHE halothane sensitive (MHEh) (n = 13) or MH normal (MHN) (n = 15) classified patients. Statistically significant differences (P < 0.05) were also found at 75 micromol/L. Exposure for 8 min yielded significant differences at 50 micromol/L only between MHS and MHEh. MHEh muscles revealed a dose-response curve similar to that found in MHN specimens. MHS muscles showed a significantly higher sensitivity to 4-CmC than either MHEh or MHN, and, in the probands tested so far, MHEh and MHN muscles seem to identically respond to 4-CmC, which seems to indicate a normal response in MHEh probands, implying no MH susceptibility. Therefore, 4-CmC might reduce the frequency of MHEh diagnosis based on standard halothane-caffeine IVCT. However, since MHE individuals may also represent an aberrant genetic status, with MH causing defects linked to unknown mutations, it is premature to consider 4-CmC as a solution to the diagnostic uncertainty of the true status of MHE probands. Presently, 4-CmC may provide supplementary information for a more precise phenotypic categorization of MHE individuals.

Clinical presentation of suspected malignant hyperthermia during anaesthesia in 402 probands

As anaesthetists have become more aware of malignant hyperthermia the mortality rate has fallen, but concommitantly the number of dubious and aborted cases has increased. All probands who developed a suspected malignant hyperthermia reaction during anaesthesia and subsequently underwent muscle biopsy were classified according to the clinical presentation. A probability for malignant hyperthermia can be calculated, using the classification, for each type of clinical presentation; this varied from 0.96 to 0.07. Certain clinical features were found to be of more value as predictors than others; these included a high creative kinase and myoglobinuria. The accuracy of prediction depends on a clear contemporaneous description of the clinical events.

[Malignant hyperthermia in Austria. I. Epidemiology and clinical aspects]

Investigation of malignant hyperthermia (MH) was started in 1975; by March 1986, 79 suspected cases had been reported. In vitro contracture tests were performed in 66 probands or their parents; in 61 of these (92%), MH was confirmed and 5 (8%) proved negative. In 4 lethal crises, the parents refused biopsy, but because of well-documented clinical histories these were also included as confirmed MH reactions. We were able to analyse 65 cases of documented MH, and 9 patients are still to be investigated. About 18% of all Austrian hospitals (29 of 158) had reported 1-14 MH reactions (mean 2.7/hospital); it must therefore be assumed that a high number of crises are either not detected or not reported, and the total incidence of MH cannot be estimated. In our hospital (the University Hospital of Vienna), the incidence was 1:23,600 (including children and adults), whereas in Bludenz (Vorarlberg), the incidence was as low as 1:1,300 (in children only). This might partly be explained by genetic factors (such as inbreeding); we identified 3 families, all from Vorarlberg (which is a small, secluded mountain area), in which both parents were carriers of the MH trait. Fulminant crises (of which three times as many were rigid as were non-rigid) accounted for 58%, and masseter spasm for 26%, of all MH reactions. There was a significant influence of sex (72% males) and age (71% less than 20 years) on incidence. Neuromuscular symptoms or other signs reported to be associated with MH were found in only 5 patients (8%). During crises, cardiac symptoms (81%) and cyanosis (71%) were frequently observed; rigidity (45%) and body temperature above 39 degrees C (27%) showed remarkably low incidences. The overall mortality was 17% (11 of 65); it was significantly increased if the maximum temperature exceeded 39 degrees C, after acute surgery or anaesthesia lasting greater than 60 min, and in patients aged over 20 y. Most crises required no specific therapy; dantrolene was administered to only 10 patients. In the future, earlier detection via better monitoring, improved documentation, and mandatory reporting of suspected MH reactions should allow a more detailed description of MH and could further decrease the mortality associated with this condition.