Risk of dementia among individuals with psoriasis: A nationwide population-based cohort study in Taiwan

Objective: Psoriasis is a chronic inflammatory disease putatively associated with dementia. However, the epidemiologic evidence of the relationship between psoriasis and dementia has been limited. We used a large national sample to investigate this relationship as well as the association between systemic therapy for psoriasis and incident dementia. Methods: The cases were identified as a first recorded diagnosis of psoriasis (ICD-9-CM codes: 696.0, 696.1, or 696.8) between 1996 and 2013 from Taiwan's National Health Insurance Research Database (NHIRD). Each selected case of psoriasis was compared with 4 sex-, age-, and urbanization-matched comparison subjects. The first diagnosis of dementia (ICD-9-CM codes: 290.0-290.4, 294.1-294.2, 331.0-331.2, or 331.82) that covered vascular and nonvascular subtypes until the end of 2013 was tracked in both groups. Cox regression analyses and a competing risk model were applied to evaluate the risk, adjusting for sex, urbanization, age, hypertension, diabetes, heart disease, hyperlipidemia, stroke, and depression. The association between systemic therapy and incidence of dementia in the psoriasis group was examined in further stratified analyses. Results: Overall, 3,820 patients with psoriasis and 15,280 comparisons were identified. After adjustment, a significantly higher risk of dementia was identified in the psoriasis group than in the comparison group (adjusted hazard ratio [aHR] = 1.23; 95% CI, 1.06-1.42). A significant association between psoriasis and dementia was identified for nonvascular dementia (aHR = 1.25, 95% CI, 1.07-1.45) but not for vascular dementia (aHR = 1.27, 95% CI, 0.83-1.93). Receiving systemic therapy for psoriasis for more than 90 days significantly reduced the risk of developing dementia compared with no systemic therapy (aHR = 0.66; 95% CI, 0.45-0.97). Compared with those who received no systemic therapy, the patients who received disease-modifying antirheumatic drugs and/or biologics had a significantly lower risk of dementia incidence (aHR = 0.69; 95% CI, 0.50-0.97), which was not the case in patients who received only phototherapy. Conclusions: Individuals with psoriasis have a significantly higher incidence of dementia, particularly the nonvascular type. Systemic therapy might be protective in preventing dementia in patients with psoriasis.