Background Although psoriasis and chronic periodontitis (CP) may share an underlying immune dysregulation as part of their pathologies, to date only one small-scale cross-sectional pilot study has investigated the potential association between CP and psoriasis. Objectives This study aimed to investigate the subsequent risk for psoriasis following a diagnosis of CP by utilizing a cohort study design and population-based dataset in Taiwan. Methods In total, 115 365 patients with CP were included in the study cohort and 115 365 patients without CP were included in the comparison cohort. We individually tracked each patient for a 5-year period to identify those who had subsequently received a diagnosis of psoriasis. A Cox proportional hazards regression was performed to compute the 5-year risk of subsequent psoriasis following a diagnosis of CP. Results We found that the incidence rate of psoriasis during the 5-year follow-up period was 1·88 [95% confidence interval (CI) 1·77-1·99] per 1000 person-years in patients with CP and 1·22 (95% CI 1·14-1·32) per 1000 person-years in comparison patients. After censoring those who died during the follow-up period, and adjusting for monthly income and geographical region, compared with comparison patients, the hazard ratio (HR) of psoriasis for patients with CP was 1·52 (95% CI 1·38-1·70). Furthermore, the study subjects who had undergone a gingivectomy or periodontal flap operation had only a slightly higher adjusted risk of psoriasis than comparison patients (HR 1·26). Conclusions This study detected an increased risk for psoriasis among patients with CP. Treatment for CP attenuated, but did not nullify, the risk for subsequent psoriasis.
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