Radiculopathy in neuromyelitis optica. How does anti-AQP4 Ab involve PNS?

Background Until recently, the peripheral nervous system (PNS) had been known to be spared in multiple sclerosis (MS) and neuromyelitis optica spectrum disorder (NMOSD). However, some studies of late have reported PNS damage in demyelination diseases of the central nervous system (CNS) such as MS and NMOSD. Although multiple studies have reported characteristics reminiscent of peripheral neuropathy in MS, there have been limited reports in NMOSD. To investigate the incidence and pathology of peripheral neuropathy in NMOSD, we reviewed articles describing such cases including our own case. Methods We performed a search of all clinical studies of peripheral neuropathy in NMOSD published up to December 17, 2016. We put no restrictions on language or year of publication in our search. The following keywords were searched: radiculopathy, peripheral nervous system diseases, neuromyelitis optica, neuromyelitis optica septrum disorder, aquaporin 4, electrodiagnosis, neural conduction and electromyography. Result We review ten cases (nine published reports and our own case study) of peripheral neuropathy in NMOSD. Each case could be confirmed as radiculopathy by electrodiagnostic (EDX) testing. Presently, there are two disparate viewpoints on peripheral neuropathy in NMOSD. In the first, aquaporin 4, which exists in the transitional zone of the CNS-PNS at the root level, may be the target of radiculitis in NMOSD. In the second, there may be some other unknown antibody to an axoglial antigen or something else that may play an active role in PNS damage. In our survey of ten case studies, the EDX results confirmed mixed axonal loss as well as demyelination type radiculopathy, which lends support to the first viewpoint. Conclusion Pathophysiology of PNS damage in NMOSD might be due to radiculopathy. Although it seems to be rare, radiculopathy may actually be underestimated, and correspondingly underreported, due to its overlap with symptoms of myelitis. Therefore, further evaluation is needed to establish the incidence and pathophysiology of radiculopathy in NMOSD.