Absence of correlation between infantile hypotonia and foramen magnum sizein achondroplasia

Virtually all infants with achondroplasia ibly severe hypotonia in infancy. This hypotonia contributes to delays in motor development and risks for su dden death. Some have proposed that this hypotonia is a direct result of im paired function of long tracts of the spinal cord, secondary to the intrins ic narrowing of the foremen magnum, which also is present in variable sever ity in all children with achondroplasia. We postulated that if foraminal co nstriction causes infantile hypotonia, then there should be a strongly posi tive correlation between foraminal size and severity of hypotonia. Therefor e, clinical and computed tomographic data in 71 infants were retrospectivel y reviewed. We found no correlation. These results suggest that there is no direct relationship and foraminal size does not affect severity of hypoton ia. Other potential explanations for this infantile hypotonia are considere d. (C) 2001 Wiley-Liss, Inc.