Diagnostic profile of neonatal hypotonia: an 11-year study.

The profile of disorders presenting with neonatal hypotonia to the neonatal intensive care unit has not been studied previously. An 11-year retrospective cohort study of neonates, who were identified through computer database records and were admitted to the Neonatal Intensive Care Unit from January 1989 to December 1999 at the Montreal Children's Hospital (Montreal, Québec), is presented. The final diagnoses, tests obtained, and outcome were determined from a structured review of the subject's hospital record. The database search generated 95 records, of which 50 neonates met the inclusion criteria. The hypotonia was classified as central in 33 patients (66%) and peripheral in 17 (34%). Hypoxic-ischemic encephalopathy (n = 13), Prader-Willi syndrome (n = 6), myotonic dystrophy (n = 6), other muscle disorders (n = 6), chromosomal disorders (n = 4), and peripheral nerve disorders (n = 3) were the most common diagnoses. The genetic tests of highest yield were fluorescent in situ hybridization for Prader-Willi syndrome, DNA methylation studies for Prader-Willi syndrome, trinucleotide repeat testing for myotonic dystrophy, and karyotype analysis. A diagnostic approach is proposed based on the results.