Lower motor neuron involvement in patients with neuromyelitis optica spectrum disorders

Involvement of the central gray matter of spinal cord is a characteristic magnetic resonance imaging (MRI) feature of aquaporin-4-immunoglobulin G antibodies (AQP4-IgG) positive neuromyelitis optica spectrum disorders (NMOSD). However, there has been no systemic electrophysiological study investigating the frequency of lower motor neuron involvement in NMOSD patients.

We retrospectively reviewed a cohort of 59 NMOSD patients with results of concentric needle electromyography (EMG) and nerve conduction studies (NCS) that were admitted to the Department of Neurology of Chinese PLA General Hospital between January 2016 and December 2019.

Acute and/or chronic denervation was found in 22.0% (13/59) of the NMOSD patients by EMG. Peripheral or cranial neuropathy indicated by abnormal NCS changes was found in 11.9% (7/59) of the NMOSD patients. Denervation indicated by EMG that can be accounted for by abnormal NCS was found in 6.8% (4/59) of the NMOSD patients, while 3.4% (2/59) of the NMOSD patients had NCS abnormality without denervation indicated by EMG. Accordingly, 9 of the 59 NMOSD patients (15.3%) had lower motor neuron involvement, and moreover, 6.8% (4/59) of the NMOSD patients had corresponding spinal cord or brainstem lesions on MRI.

Not uncommon lower motor neuron involvement exists in NMOSD patients, so needle EMG and NCS studies should be performed in NMOSD patients with suspected lower motor neuron involvement.