Preservation of the phrenic motoneurons in Werdnig-Hoffmann disease.

A neuropathological study on spinal cords at the third, fourth, and fifth cervical levels in 4 patients with Werdnig-Hoffmann disease revealed marked, generalized loss of motoneurons except for a cluster of large or medium-sized ones in the most medial portion of the anteromedial cell group. These well-preserved neurons were regarded as the phrenic motoneurons because diaphragmatic movement was the only muscle activity that remained until the last stage of illness. Furthermore, in its location and its cytoarchitectonic and neuronal characteristics, this neuronal cluster coincides with the phrenic nucleus as previously localized in the spinal cords of patients with phrenicotomy.