A large propensity-matched EHR study finds that systemic autoimmune diseases broadly increase cerebrovascular risk (TIA, ischemic stroke) and show a more variable, disease-dependent association with incident Parkinson's and Alzheimer's disease; systemic corticosteroids had limited impact on…

This paper signals that systemic inflammation and vascular comorbidity are important stratifiers and potential modifiable risk axes for PD research—supporting vascular surveillance, cohort stratification, and targeted mechanistic work on inflammation–vascular interactions rather than immediate…

Systemic autoimmune diseases (AIDs), characterized by chronic peripheral inflammation and frequent vascular comorbidity, are increasingly linked to adverse central nervous system (CNS) outcomes; however, comparative evidence across diverse AIDs and clarification of the roles of vascular burden, inflammatory activity, and immunomodulatory therapy remain limited. Using the TriNetX Global Collaborative Network, we conducted a sequence of retrospective, propensity score-matched cohort experiments in adults aged 50-85 years to quantify incident Parkinson's disease (PD), Alzheimer's disease (AD), transient ischemic attack (TIA), and ischemic stroke across 22 AIDs and to evaluate therapy- and inflammation-stratified risk patterns. In the primary disease-control analysis (Experiment 1 A), AID diagnosis was associated with broadly elevated neurodegenerative and cerebrovascular risk, with stronger and more consistent associations for TIA and ischemic stroke than for PD and AD. To probe robustness, we repeated analyses under tighter control of baseline vascular burden (Experiment 1B: additional matching on circulatory-system diagnoses) and under treatment balancing (Experiment 1 C: additional matching on immune-suppressant exposure). Vascular matching substantially attenuated many associations, particularly for AD, whereas immune-suppressant matching did not materially erase the pervasive cerebrovascular excess. Within-disease CRP stratification (Experiment 2; low vs elevated CRP) did not yield a uniform neurodegenerative gradient but identified a disease-dependent ischemic vulnerability axis in selected inflammatory phenotypes. In treatment substudies, systemic cortisone exposure (Experiment 3) showed little association with PD/AD risk but a modest, heterogeneous increase in TIA/ischemic stroke. Medication-specific strata (Experiment 4) revealed stronger but directionally variable separations, consistent with confounding by indication and severity. Together, these findings position systemic autoimmunity as a robust marker of heightened cerebrovascular risk and a more phenotype-dependent correlate of neurodegenerative risk, supporting intensified vascular surveillance in high-risk AID populations and mechanistic work disentangling inflammation, comorbidity, and treatment.