[31P-NMR spectroscopy of mitochondrial myopathies: the relation between abnormal energy metabolism and muscle biopsy findings].

31P-NMR spectra were obtained from the quadriceps femoris muscle (at rest and after aerobic exercise) of the 7 cases of mitochondrial myopathies (2 cases of mitochondrial encephalomyopathy and lactic acidosis(MELA), 1 case of myoclonus epilepsy with regged red fiber, 1 case of Kearns-Sayre syndrome, 3 cases of progressive external ophthalmoplegia), using superconducting whole body MR (Magnetom, Siemens). One case showed abnormally low Pcr/Pi ratio in the resting state. An aerobic exercise using ergometer was performed on the other 6 patients. Three of them demonstrated significant reduction and delayed recovery of the Pcr/Pi ratio after exercise. This reduction was not detected in the control subjects. Histological studies of biopsied muscles revealed ragged red fibers in all the cases, the number varies, however, from 0.5 to 15.3 per cent of the total fibers. Abnormalities in the Pcr/Pi ratio of phosphorus spectra, in resting state or after exercise, tend to be observed in patients showing abundant ragged red fibers. Focal cytochrome c oxidase deficiency with relatively small amount of ragged red fibers (less than 10 per cent of the total fibers) was histologically noted in five of our patients, excluding 2 MELA patients. Biochemical assay of mitochondria enzyme was normal. It has been assumed that these patients have no primary defect in energy metabolism and the occasionally observed cytochrome c oxidase deficient fibers are non-specific findings probably caused by some devastating process occurring in these fibers. However, our present studies revealed abnormal reduction and delayed restoration of the Pcr/Pi ratio in 2 out of 5 focal cytochrome c oxidase deficiency cases.(ABSTRACT TRUNCATED AT 250 WORDS)