All the included studies reported higher levels of inflammatory markers, IgG levels of periodontal bacteria, and/or clinical parameters of periodontitis with the two concomitant diseases (some neurodegenerative disease and periodontitis), compared with the diseases isolated (summarized in Figure 2). Despite that we found some minor problems in domains in the qualitative analysis, all the studies have consistent and valid information and were judged to be at low risk of bias. However, when we analyzed the body of the evidence, some problems regarding the imprecision and inconsistency hindered the accuracy of the evidence, alerting us to interpret cautiously the results. CLICK TO REVIEW