Objective: The aim of this review is to summarize the clinical and paraclinical findings that demonstrate that multiple sclerosis (MS) affects the peripheral nervous system (PNS) as well as the central nervous system (CNS). 

Methods: Narrative review.

Results: MS is traditionally defined as a chronic demyelinating immune-mediated disease of the CNS. However, there is emerging evidence that MS is a disease that does not solely affect the CNS but can manifest with PNS involvement as well. Several pathology studies have reported on signs of demyelination in the PNS, as well as on structural and functional involvement of the PNS in persons with MS (pwMS). From the functional aspect, several studies have shown autonomic nervous system (ANS) involvement in the form of sudomotor dysfunction measured with quantitative sudomotor axon reflex test (QSART) in different stages of MS, adding to the growing body of evidence that indicate PNS involvement in MS. In this review the clinical, pathological, neurophysiological, and imaging findings that demonstrate that MS affects the PNS as well as the CNS are summarized, with the emphasis on the ANS abnormalities.

Conclusions: Further large-scale research is needed in order to fully understand the frequency and importance of PNS affection in MS.