Researchers found that lower motor neuron involvement is not uncommon in patients with neuromyelitis optica spectrum disorders (NMOSD), as published in Multiple Sclerosis Related Disorders.

The team retrospectively reviewed the results of a cohort of 59 patients with NMOSD who had both concentric needle electromyography (EMG) and nerve conduction studies (NCS) performed between January 2016 and December 2019.

The EMG studies showed acute and/or chronic denervation in 22% of the patients with NMOSD, and 11.9% of the patients showed peripheral or cranial neuropathy based on abnormal NCS results. NMOSD is known to involve the central gray matter of the spinal cord, but to date, few electrophysiological studies had investigated lower motor neuron involvement in these patients.


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“When lower motor neuron involvement (atrophy/weakness and/or reduced deep tendon reflex) was suspected in the patients, [EMG] and [NCS] were performed during hospitalization,” the researchers wrote.

“EMG showed signs of acute and/or chronic denervation in 13 of 59 (22%) NMOSD patients, while both normal and abnormal NCS were found among them.”

These results suggest that the denervation observed could be secondary to focal peripheral neuropathies or to motor neuron damage. The mechanisms underlying the abnormalities found in the NCS are not clear; however other studies have reported improvements in peripheral neuropathy after immunotherapy in come cases of neuromyelitis optica, suggesting there might be an immune-mediated mechanism.

Due to the frequency of the finding of denervation in patients with NMOSD in their study, the authors recommend conducting needle EMG and NCS studies in patients with NMOSD in whom lower motor neuron involvement is suspected.

Reference

He M, Yang F, Wu L et al. Lower motor neuron involvement in patients with neuromyelitis optica spectrum disorders. Mult Scler Relat Disord. Published online January 20, 2022. doi:0.1016/j.msard.2022.103544