Microphotometric enzyme assay in single muscle fibers was performed on two patients with lactic acidosis. Neither case showed ragged red fibers upon histochemical evaluation. Biochemical analysis of mitochondrial enzymes demonstrated low normal cytochrome c oxidase (COX) activity in Case 1 and deficient COX in Case 2. Quantitative single muscle fiber analysis in patients showed marked variation in COX activity in Case 1, reflecting mosaic distribution of fibers with near-normal COX activity and with defective COX activity. These data suggest that this microphotometric assay may be valuable for elucidating the significance of 'partial enzyme deficiency'. In addition, this assay method may be applied to needle biopsy specimens.
Acidosis, Lactic Adolescent