Congenital muscular dystrophies and unstructured congenital myopathies.

A satisfactory nosological classification of all congenital myopathies without structural characteristics is not yet available. The term "congenital dystrophy" does not describe one but at least three disease states, of which the Fukuyama type and the Ullrich type are entities defined by clinical and morphological criteria. Some patients with nonprogressive dystrophic changes may show marked abnormalities in size and distribution of fiber types. "Congenital fiber type disproportions" has been defined as a pattern with many small type I fibers and few large type II fibers. A similar pattern can be found in the rigid spine syndrome. Other abnormal histometric patterns (e.g. predominance of small and large type I fibers, type II fiber atrophy in combination with congestive cardiomyopathy) are not infrequently encountered. The application of a prefabricated diagnostic label should be reserved for cases fulfilling strictly defined morphological and clinical definitions. In the rest, objective description of findings may still be the only appropriate diagnostic approach.