[Reducing body myopathy--ultrastructure and classification (author's transl)].

Reducing body myopathy is a very rare progressive muscular disease. Apart from a non-specific circumscribed muscle fiber degeneration it displays muscle fiber inclusions which have reducing properties as a typical morphological feature. The nosological classification of the disease is not settled. A case in a 15 years old girl is reported. She suffered from a progressive muscular weakness and atrophy and in a muscle biopsy regressive changes were obvious. Furthermore, multiple eosinophilic muscle fiber inclusions were also observed, which exhibited reducing properties. They consist of electron dense granules with a diameter of 12--16 nm. Since a sister of the patient has suffered for many years from a clinically and morphologically similar muscle disease, reducing body myopathy apparently belongs to the group of congenital myopathies with structural abnormalities. Muscle fiber inclusions with reducing properties also occur in another myopathy, in which they structural and histochemical differ widely from those found in reducing body myopathy. The reducing body myopathy is better named after its typical morphological property, the granular inclusions. It is proposed to name it "granular body myopathy".