PD and MS are traditionally considered distinct neurological disorders, but emerging evidence suggests potential overlapping mechanisms. Clarifying their temporal associations may provide insight into shared pathophysiology and inform clinical practice.

A systematic review of the PubMed database was conducted to identify population-based studies examining the temporal association between PD and MS, including NMOSD. Studies were included if they reported incidence data for MS following PD (PD→MS), PD following MS (MS→PD), or PD following NMOSD. Nine eligible studies were identified. A meta-analysis was performed on five studies with complete comparator data using a random-effects model (DerSimonian-Laird estimator), with risk ratio (RR) as the summary measure. Subgroup analyses were conducted for each direction of association. Publication bias was assessed using Egger’s test, Begg’s test, trim-and-fill method, and fail-safe N calculations (Rosenthal, Orwin, and Rosenberg approaches).