[Ultrastructural study of the oculomotor muscle in 2 familial cases of Steinert's disease].

A biopsy specimen of an extra-ocular muscle from a brother and sister affected by typical familial Steinert's disease was examined by electron microscopy. Considerable disorganisation of the contractile element was observed with a gross accumulation of abnormal mitochondria. This was a very different appearance to the findings observed in skeletal muscle in Steinert's disease and much closer to the findings in skeletal muscle in certain 'ocular' myopathies. One cannot fail to be impressed by the discordance between the appearance of the muscular disorganisation and the rarity of clinical oculomotor disturbances in this disease.