[Dystrophia myotonica (Steinert disease)--a frequently misdiagnosed disease]

Dystrophia myotonica (Steinert's disease) is the most common hereditary disease of the neuromuscular system in adults. Its mode of inheritance is autosomal dominant. The gene responsible for its is located on chromosome 19 in the linkage domain of the loci for the apolipoproteins C2, C1 und E and of the creatine kinase of skeletal muscle (CKMM). Myotonic dystrophy is categorized in an adult and in a congenital form. In the adult form, the characteristic findings are muscular atrophy in certain regions of the body (face, neck and distally in the extremities) and myotonia. Cataract, intraocular hypotension, gonadal atrophy, conduction abnormalities in the heart and hearing deficiencies appear quite often in the course of the disease. In the congenital form, general muscle weekness (particularly pronounced in the face) is the leading finding, combined with retarded loco motor and mental development. A decisive criterion for the diagnosis of this form is the occurrence of myotonic dystrophy in the patient's mother. Electromyographic investigation is indicated when a suspicion of myotonic dystrophy cannot be ascertained on the basis of clinical and genetic findings. Myotonic runs in the EMG will then corroborate the suspicion. Recent electrophysiological investigations have indicated that at least three different types of channels for the passage of ions through the membrane of the skeletal muscle cells show abnormal behaviour, i.e. the channel for Cl-, Na+ and K+. These findings corroborate the hypothesis that the abnormality responsible for myotonic dystrophy is situated in the membrane systems. A pharmacological treatment of the muscular dystrophy has not yet been developed.(ABSTRACT TRUNCATED AT 250 WORDS)