Background: Neonatal hypotonia is a common request for neurological consultation. The aim of this study is to describe the main clinical features of muscular hypotonia in newborns at the light of the histopathological findings.
Methods: We reviewed 50 medical records of hypotonic neonates with abnormal muscular biopsy. In all of the cases, the serum concentration of creatine kinase was determined and biopsies were examined by a qualified neuropathologist.
Results: The most frequent muscular cause of neonatal hypotonia was specific congenital myopathies (23 cases), followed by congenital muscular dystrophy (15 cases), congenital myotonic dystrophy (eight cases) and metabolic myopathies (four cases). The most common specific congenital myopathy was fiber type disproportion (10 cases). The association with joint contractures and the involvement of respiratory muscles were frequent; respiratory complications were the first cause of death.
Conclusions: Muscular biopsy is required for the definitive diagnosis of specific congenital myopathies, congenital muscular dystrophy and metabolic myopathies. In congenital myotonic dystrophy, the mother is almost always affected; neonates with specific congenital myopathies and congenital muscular dystrophy can be very similar to those with congenital myotonic dystrophy; the examination of the mother, specially a careful search for myotonia, is the best diagnostic clue; if there are signs of myotonia, the diagnosis can be made by molecular genetic study.