Muscle

P31 NMR spectroscopy is useful for the diagnosis of some myopathies and it is necessary to further specify its range of application. Mitochondrial myopathies show one or more abnormalities, yielding a heterogeneity of results that may correspond to their biochemical heterogeneity. We here report on a rare mitochondrial disease due to a defect in the protein X of the pyruvate dehydrogenase complex. The abnormalities observed by muscle P31 NMR were mainly low phosphocreatine (PCr) and high inorganic phosphate at rest and too small acidification with exercise. The patient thus showed 2 of the main abnormalities described, alone or in association, in mitochondrial myopathies. The rate of PCr recovery was normal. P31 NMR thus seems sensitive in this precise defect and can help the clinician for the diagnostic process. It is however too early to conclude whether P31 NMR abnormalities are specific for precise mitochondrial defects. This search for diagnostic specificity could also benefit from other NMR approaches