Hypotonia in the Newborn Infant.

Neonatal hypotonia, defined as hypotonia present from birth to 4 w of age, has a plethora of causes. Distinguishing between central and peripheral causes is the key to arriving at a timely diagnosis. A thorough history, general and neurologic examination, and systematic utilization of laboratory and ancillary studies allow for rapid diagnosis in most cases. Strategic use of genetic testing yields a definitive diagnosis in some cases. Arriving at a diagnosis may afford rapid treatment initiation, with the potential to change prognosis.