[Central core disease. Two cases with histoenzymology, electron microscopy and review of the literature (author's transl)].

Central axis myopathy is one of the commonest congenital myopathies. It is transmitted above all by a dominant autosomal mode, but sporadic cases are numerous. Clinically, it is characterised by neonatal hypotonicity, delayed slow motor development in the young child, but the diagnosis may be mode only in adult life. There is preferential involvement of the muscles of the pelvis girdle, muscle wasting otherwise remaining moderate in general. Various skeletal malformation are fairly often present in association. the electromyogram is of myogenic type. The disorder does not show any marked progression. By light microscopy, the central axis is more clearly seen by stains such as PAS, trichromes, and haematoxylin phospho-tungstic. In most cases it is the sole finding and is seen in a variable number of fibres, not only from one patient to another, but from one muscle to another. The rest of the fibre may be normal or show various lesions with no specific characteristics. Histoenzymology may show rarefaction or disappearance of the II fibres, relative hypotrophy of I or II fibres, or the absence of any oxidative phosphorylase activity in the central axis. The latter shows changes with regard to ATPase activity ("structured core" and "non-structured core"). Electron microscopy shows changes in varying degree in the axis, possibly to the extent of myofibrillary destruction, contrasting with the absence of or only slight changes in the rest of the fibre. Two cases, one in a child and the other in a 24-year-old woman, are reported, illustrating the above findings. Various interpretations have been suggested for this condition. Certain authors accept the existence of progressive transformation of the II fibres, whilst others describe pathology of the Z striae or a disturbance in the distribution of the mitochondria. Similarities with other muscular lesions, in particular rod myopathy, have been envisaged.