Loss of Motor Neurons Innervating Cervical Muscles in Patients With Multiple System Atrophy and Dropped Head.

We investigated whether loss of motor neurons innervating the neck muscles contributes to dropped head (DH) in multiple system atrophy (MSA). From 75 patients with autopsy-proven MSA, we retrieved 3 who had DH (MSA-DH), and examined the 4th cervical cord segments. Neurons of the medial and lateral nuclear groups (MNG and LNG) innervate the neck and shoulder muscles, respectively. We measured the area of individual neurons in the MNG and LNG, and created an area-frequency histogram. Neurons were classified as large or small based on their area, and their total numbers in the MNG and LNG were counted. In the MNG, the numbers of both total neurons and large neurons were significantly lower in MSA patients than in the controls (214.2 ± 91.4 vs 521.3 ± 74.8, p = 0.0030, and 26.2 ± 9.1 vs 88.0 ± 34.6, p = 0.020, respectively), and were significantly lower in MSA-DH than in MSA-nonDH (139.7 ± 7.6 vs 288.7 ± 74.6, p = 0.048, and 18.0 ± 4.1 vs 34.3 ± 4.1, p = 0.016, respectively). There were no differences in the LNG neuron counts between the MSA-DH and MSA-nonDH groups. Loss of cervical motor neurons may be responsible for DH in MSA.