Congenital myopathie are rare diseases characterized by weakness that is usually relatively mild but persists throughout life, either slowly or remaining stationary.This diseases account for one of the top neuromuscular disorders.
Etiology.
The cause is not known. A few of these disorders are familial and are suspected of having a genetic basis, but so many cases are sporadic that other causes are not exclude, and there are no clear clues.
Pathology of Congenital Myopathie.
These diseases are defined in terms of pathology, and most of them have been delineated within the past decade since the introduction of histochemical techniques to study muscle biopsy. The names of the diseases reflect the predominant anatomic disorder. In central core disease, the central portion of the muscle fiber appears rather amorphous, in contrast to the fibrillate appearance of the surrounding normal portion. In cross section,the central portion appears blue when stained with Gomori’s trichrome, in striking contrast to the red periphery. The central areas lack all oxidative enzyme activity, and there are no mitochondria in this region. In nemaline myopathy or rod myopathy, small threadlike or rod bodies are scattered throughout the fiber.
The rods are barely visible in conventional hematoxylin and eosin stains, but can be seen readily in phase contrast or with the trichrome stain. In electron microscopy the structures seem to originate in the Z-band, and circumstantial evidence suggests that they are composed of tropomyosin. Myotubular myopathy designates the appearance of myofibers that resemble a stage in the early development of fetal muscle, with nuclei located centrally rather than at the periphery and surrounded by a halo of apparently empty space.
Because the pathogenesis of this appearance is uncertain, some investigators prefer the name centronuclear myopathy. In other disorders mitochondria have appeared abnormal, either in number (too many) or size (too large), often associated with accumulations of lipid droplets.
Clinical Manifestations
Although designated “congenital,” these disorders are only exceptionally symptomatic in the first year of life, except that the onset of walking may be delayed. Later, the symptoms of proximal limb weakness become evident: waddling gait, difficulty in climbing stairs, frequent falls, and scoliosis. Later, there may be weakness of the arms. There are few clinical clues to each specific histologic abnormality. Among the nemaline cases there have been skeletal abnormalities (kyphoscoliosis, pigeon breast, pes cavus, high palate, and an unusually elongated face); In two families with myotubular disease, ophthalmoplegia was present as well as limb weakness. Central core and mitochondrial disorders have not been associated with distinctive clinical signs other than proximal limb weakness.
Diagnosis of Congenital Myopathie
Proximal limb weakness in a young child is usually myopathic in origin, but must be distinguished from the neurogenic Wohlfart- Kugelberg-Welander syndrome and from polyneuritis. Myopathic abnormalities in the EMG, an abnormal family history, an incidence in girls, and especially the histologic abnormalities define the individual entities. The serum enzymes may be normal or slightly increased. In some clinics most cases of apparently congenital myopathy fail to meet the specific histologic criteria, showing only nonspecific myopathic changes in biopsy. There is no better designation for these cases than “congenital myopathy,” but it is likely that there is more than one cause.
Treatment And Prognosis
There is no specific treatment for any of these disorders. Physical therapy and orthopedic corrective measures are of value. There are too few cases to generalize about the course of this illnesses;most seem to be mild and non-progressiveness,but occasional cases are more severe.
