THE HYPOTONIC INFANT. A REVIEW.
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Skeletal muscles from four infants with a severe neonatal form of myotonic muscular dystrophy showed histopathologic features of immaturity. Three of the infants died in the neonatal period and were studied at autopsy; one of these and the still-living infant had a gastrocnemius muscle biopsy. The most severely involved muscles were those associated with arthrogrypotic joints regardless of function as flexors or extensors. Pharyngeal muscles and the diaphragm were also severely involved. Immature features included irregularly distributed small, round muscles fibers with large vesicular internal nuclei and sparse myofibrils. Histochemical differentiation was incomplete and fiber types often could not be distinguished. Muscle fiber degeneration and other features of myotonic dystrophy in adult muscle were lacking. Electron microscopy showed fine granular chromatin and convoluted nuclear membranes of centronuclear fibers, dialated transvers tubules that were aligned longitudinally as in fetal myotubes, poorly formed Z-bands, simple mitochondria, and many satellite cells. We suggest that these features represent an arrest in fetal muscle maturation due to unresponsiveness of an abnormal sarcolemma to trophic influences of normal innervation.
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We describe a child with whistling face and multiple contractures, including ulnar deviation of fingers, compatible with a diagnosis of Freeman-Sheldon syndrome (FSS). This patient also presented severe hypertonicity, multiple episodes of pneumonia, difficulty in swallowing, and poor weight gain, which are characteristic of the most severe cases of FSS. A brain CT scan showed cerebellar and brainstem atrophy. Auditory brainstem responses were absent. The child died at 5 months of respiratory failure. This case suggests the possibility that, especially in the most severe forms, brain abnormalities may be responsible for some of the clinical manifestations of this syndrome, i.e., respiratory problems, difficulty in swallowing and severe hypertonicity. We assume that there is more than one pathogenetic mechanism (muscular, skeletal, and neurological) underlying FSS, which, together with the genetic heterogeneity and the wide range of clinical symptoms leads us to suggest that it is more appropriate to speak of a Freeman-Sheldon spectrum rather than syndrome and that thorough investigation for CNS and auditory abnormalities should be part of the initial work-up of these patients.