Résumé :
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Communication n° 50. Congenital myopathies are characterized by the presence of distinctive structural and histochemical diagnostic features with type 1 predominance and/or hypotrophy but diagnosis may be inconclusive at muscle biopsy during early age. In some central core disease(CCD), cores appear to increase with age and may not be found in young patients. A recessive form of CCD may transiently present as multiminicore disease (MmD) at early age. Progressive internalization of nuclei in sequential biopsies in Centronuclear Myopathy (CNM) has been described, as well as concomitant occurrence of numerous central nuclei within muscle fibers containing minicores, posing differential diagnosis between MmD and CNM. MmD genetic basis has been partially elucidated by identification of mutations of selenoprotein gene (SEPN1) in the large majority of the classical form and homozygous mutations of RYR1 in a few patients, while for CNM it remains unknown. We report two cases posing differential diagnosis and/or presenting progressive morphological changes at biopsy: 1) an 18-year-old female with early onset congenital myopathy with hypotonia, facial involvement with ophthalmoplegia and hands hyperlaxity, who required 3 biopsies from 14 months to 15 years showing progressive atrophy of type 1 muscle fibers with 18% internal nuclei and abundant multiminicores. 2) a 9-year-old male with weakness of early onset, respiratory insufficiency, facial involvement with ptosis and ophthalmoplegia and sequential biopsies at 3 and 7 years, showing type 1 fiber atrophy and progressive internalization of nuclei from 7% to 35% consistent with CNM with some Z line streaming. Multiminicore lesions and central nuclei may not represent a primary abnormality, but occur during the course of the disease, secondary to abnormal contraction related to the genetic/protein defect. Mild forms of Myotubular Myopathy may pose clinical/morphological differential diagnosis with CNM. DNA studies are in progress.
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