[Steinert's myotonic dystrophy and Thomsen's congenital myotonia. Observation of a family (author's transl)].

The nosographic relationship between Thomsen's and Steinert's disease is still uncertain. There is not agreement in the literature whether these are two different diseases or just different stages in the evolution of a single one. Four members of a family in two generations have been studied: two have a typical Steinert's, one a Thomsen's disease and one a clinical pattern that cannot be clearly considered neither of the first nor of the second type. In this patient a generalized muscular hypertrophy was followed, at the age of 54, by a generalized impairment of the muscular trophism and evolved into a severe wasting. This may be interpreted as an evolution of Thomsen's into a Steinert's disease. Furthermore, the presence in the same family of cases of both Thomsen's and Steinert's disease supports the hypothesis of a single disease. The present study suggests that Thomsen's and Steinert's diseases could be two clinical varieties of a single disease in different stages of development. This conclusion is supported by the similarity in the electromyographic patterns and in the histological picture from muscle biopsy of all patients examined.