Morphometric analysis of skeletal muscle fibres and capillaries in mitochondrial myopathies.

A morphological and quantitative study of skeletal muscle fibres and of capillary supply was performed on needle and open biopsies of quadriceps femoris muscle from 40 patients with chronic progressive external ophthalmoplegia (CPEO) with partial deficiency of cytochrome c oxidase (COX). Muscle biopsies from 5 healthy adult subjects were used as control. The study was carried out by light and electron microscopy, using an Automatic Interactive Image Analysis System (IBAS I,II). A significant decrease in fibre diameters and preferential type I fibre atrophy was seen. Red ragged fibres and fibres with cytoarchitectural changes after enzyme-histochemical reactions for detection of oxidative activities were also observed. Seventy per cent of affected fibres showed an intense subsarcolemmal rim of oxidative activity corresponding to ultrastructural accumulation of enlarged, polymorphous mitochondria in subsarcolemmal areas. The study of the capillary distribution in muscle revealed a reduction of the number of capillaries per fibre and surrounding a fibre. The primary metabolic error of the disease with defects in the oxygen utilisation, the fibre atrophy and the muscle disuse are the possible variables influencing the capillary number in CPEO patients.