Infantile centronuclear myopathy. Evidence suggesting incomplete innervation.

A male case of centronuclear myopathy is reported, with severe weakness at birth and death at 7 weeks. In all the muscles studied the fibres, despite their immature appearances, showed normal histochemical differentiation into type I and type II moieties. In contrast to the extrafusal fibres, the intrafusal fibres seemed to be normal in their development. Although the small centrally-nucleated muscle fibres were equipped with motor end-plates, the EMG revealed profuse fibrillation activity. The conflicting findings are postulated to arise from the presence of inexcitable neuromuscular junctions which nevertheless permitted a neurotrophic influence to be exerted on the muscle fibres.