Improved noninvasive diagnostic testing for malignant hyperthermia susceptibility from a combination of metabolites determined in vivo with 31P-magnetic resonance spectroscopy.

BACKGROUND

Phosphorus magnetic resonance spectroscopy (31P-MRS) in vivo has been suggested recently as a possible noninvasive diagnostic test in malignant hyperthermia (MH) susceptibility. However, differences between protocols and also within subjects may have led to inconsistent MRS abnormalities reported during and after exercise. The aim of the current study was to detect discriminant abnormalities in the leg muscles using in vivo 31P-MRS during the rest period.

METHODS

Fourteen patients shown to be MH-susceptible and 22 patients MH-negative on the basis of in vitro caffeine/halothane contracture tests according to the European MH group protocol were compared to 36 control subjects using in vivo 31P-MRS during the rest period. A score of MRS combined abnormalities was calculated from a stepwise discriminant function analysis.

RESULTS

The MH-susceptible group had a significantly (P < 0.01) higher inorganic phosphate (Pi) to phosphocreatine (PCr) (Pi/PCr) value (0.134 +/- 0.022) than either the MH-negative (0.097 +/- 0.016) or the control (0.101 +/- 0.017) group. The MH-susceptible group also exhibited a significantly (P < 0.01) higher phosphodiesters (PDE) to PCr (PDE/PCr) value (0.093 +/- 0.056) than either the MH-negative (0.034 +/- 0.021) or the control (0.029 +/- 0.019) group. Combining both MRS parameters, 13 of the 14 MH-susceptible patients demonstrated abnormal MRS test results (score value < 1.65). Conversely, 21 of the 22 MH-negative patients had normal MRS results (score value > or = 1.65). The sensitivity and specificity of this threshold value were 93 and 95%, respectively.

CONCLUSIONS

This study confirms that 31P-MRS could be useful for distinguishing noninvasively between MH-susceptible and MH-negative patients if several MRS parameter are combined. Moreover, the present MRS approach appears to be more reliable and easier than that used during exercise.