Psoriasis typically emerges among the young, while Alzheimer disease is mainly a disorder of old age, raising the question of whether psoriasis has an impact on the later development of neurodegenerative diseases.
A recent study found that the incidence of Alzheimer disease (AD) is significantly increased in patients with psoriasis, and that systemic treatment for psoriasis was associated with a reduced risk of AD.
There is overlap in psoriasis and AD, the authors noted, when taking into account T-helper (Th)1/Th17 cells. Mounting evidence has implied that abnormal immune responses, including those involving Th1/Th17 cells and cytokines, are involved in the inflammation associated with neurodegeneration in AD.
Psoriasis is a Th1/Th17-mediated chronic inflammatory skin disease; in addition, genome-wide association studies have demonstrated genetic overlap between AD and psoriasis. Other studies have suggested that psoriasis is associated with an increased risk of mental health disorders and Parkinson disease (PD).
Psoriasis typically emerges among those aged 15 to 30, while AD and PD are mainly diseases of old age, raising the question of whether psoriasis has an impact on the later development of neurodegenerative diseases.
In this study, researchers used the Korean National Health Insurance System (NHIS) database. Patients with psoriasis (n = 535,927) and age- and sex-matched controls without psoriasis (at a 5:1 ratio; n = 2,679,635) who underwent 3 or more health examinations between 2008 and 2014 were included. The median follow-up was 3.35 years.
There were 50,209 cases of AD (1.87%) in controls without psoriasis and 11,311 cases (2.11%) in patients with psoriasis.
In a multivariable-adjusted model, patients with psoriasis showed a significantly increased risk of AD (hazard ratio [HR] 1.09; 95% CI, 1.07-1.12, P < .0001) compared to those without psoriasis.
Among patients with psoriasis, the risk of AD was significantly increased in psoriasis patients not receiving systemic therapy (acitretin, methotrexate, cyclosporine, and biologic agents) compared with those receiving systemic therapy (HR, 1.10; 95% CI, 1.08-1.12 vs. HR, 0.99; 95% CI: 0.90-1.09, P < .0001).
The association was significantly stronger in middle-aged patients than in elderly patients (≥ 65 years) with psoriasis (HR, 1.30 vs. HR, 1.08).
There were some limits to the study, the authors noted. The severity of the psoriasis was not known; subjects were identified and included based on diagnostic codes; and this was a retrospective epidemiological study. In addition, other factors that could influence the development of AD, such as education level, tobacco and alcohol use, family history, and genetic factors were not known.
Kim M, Park HE, Lee SH, Han K, Lee JH. Increased risk of Alzheimer's disease in patients with psoriasis: a nationwide population-based cohort study Sci Rep. 2020;10(1):6454. doi: 10.1038/s41598-020-63550-2.