[A case of Becker type congenital myotonia with myalgia].

We reported a case of Becker type congenital myotonia with myalgia. A 28 year-old woman admitted to our hospital because of right anterior chest pain and back pain. She was diagnosed as myotonic dystrophy by other university hospital when she was 16 years old. Physical examination revealed only myotonia and could not find muscle atrophy or cataracta which were usually found in myotonic dystrophy. The quadriceps muscle biopsy revealed complete absence of type IIB muscle fiber. We diagnosed her Becker type congenital myotonia by the clinical course and family history and the histopathological findings of quadriceps muscle. Myalgia which she complained seemed to have some connection with this disease. But we could not prove the pathogenesis of this myalgia.