The incidence rates and risk factors of Parkinson disease in patients with psoriasis: A nationwide population-based cohort study

Background: The association between psoriasis and Parkinson disease has not been established. Objective: To determine the incidence rates and risk factors of Parkinson disease in patients with psoriasis. Methods: We conducted a nationwide population-based cohort study. The data from patients with psoriasis (N = 548,327, ≥20 years of age, 53.32% men and 46.68% women) and age- and sex-matched control patients (N = 2,741,635) without psoriasis were analyzed in this study. Results: The incidence rates of Parkinson disease per 1000 person-years were 0.673 and 0.768 in the control and psoriasis groups, respectively. The psoriasis group showed a significantly increased risk of developing Parkinson disease (hazard ratio [HR] 1.091, 95% confidence interval [CI] 1.029-1.115). The risk of Parkinson disease was significantly higher among the psoriasis patients who were not receiving systemic therapy (HR 1.093, 95% CI 1.031-1.159) and lower among the psoriasis patients on systemic therapy (HR 1.04, 95% CI 0.806-1.316). Limitations: The limitations of this study included the retrospective design, patient inclusion solely on the basis of diagnostic codes, and unavailability of data on confounding factors. Conclusion: Systemic anti-inflammatory agents might mitigate the risk of Parkinson disease in psoriasis patients.