Myopathy with pathological features of both centronuclear myopathy and multicore disease.

Two adult patients are described with long-standing primary myopathy characterised on light microscopy of skeletal muscle biopsy by central nuclei within muscle fibres, and on electron microscopy by multiple minicores causing sarcomere disruption. The total pathological picture is not typical of either "centro-nuclear myopathy" or "multicore disease". The apparently benign long-term prognosis of the myopathy in these patients contrasts with the severe respiratory dysfunction described in two recently reported infants affected by a pathologically similar myopathy, and justifies extensive respiratory support measures in such cases. In both cases electrophoresis of native myosin revealed only the "slow" isoenzymic forms. This finding is consistent with the overwhelming predominance of Type I fibres in the muscle biopsy. No foetal myosins, which characterize developing or regenerating muscle, were detected.