Introduction Psoriasis is a chronic inflammatory disease aff
Psoriasis is a chronic inflammatory disease affecting the skin and joints. The itch and pain caused by the skin and joint lesions affect patient quality of life. Moreover, the appearance of skin lesions often have negative impacts on patient psychological and social functions. A growing body of literature indicates that psychiatric disorders are more prevalent in patients with psoriasis. In psoriatic patients, the prevalence of depression is estimated to be 15.4%. Another study reported that pediatric patients with psoriasis have higher risks of developing depression and anxiety. The higher prevalence of depression and anxiety in psoriatic patients may be attributed to discomforts caused by lose your own voice and discomfiture caused by visible skin lesions.
The association between psoriasis and schizophrenia has not been well-established. A study reported that psoriatic patients are more likely to receive antidepressants and anxiolytics, but not antipsychotics. However, Chen et al indicated that the odds ratio (OR) of psoriasis is 1.60 in male patients with schizophrenia, while the OR of psoriasis is not significantly higher in female patients with schizophrenia. Another nationwide population-based study conducted in Taiwan showed female patients, but not male patients, with schizophrenia have increased risk of psoriasis. Given these conflicting results, the association between psoriasis and schizophrenia remains to be clarified.
Discussion While previous research showed conflicting results regarding associations between schizophrenia and psoriasis, our study showed that the prevalence of schizophrenia is higher in both male and female psoriatic patients. The prevalence ratios were significantly higher in psoriatic patients > 40-years old and in psoriatic patients with comorbidities, including cerebrovascular disease, chronic pulmonary disease, and liver disease. Within psoriatic patients, older age, cerebrovascular disease, and chronic pulmonary disease exhibited higher odds for schizophrenia. Although the trends of schizophrenia increased in both the psoriatic cohort and the general population from 2000 to 2010 (Figure 2 and Table 4), the trend in the psoriatic cohort was significantly higher (AAPC difference = 9.6, p < 0.05). Psoriasis is a chronic immune-mediated disease involving systemic inflammation. T helper 17 (Th17) cells and proinflammatory cytokines, such as tumor necrosis factor-α, play a crucial role in the microenvironment of psoriasis. Th17 cells and proinflammatory cytokines are also involved in the pathogenesis of schizophrenia. Activation of Th17 cells occurs in patients with drug-naive, first-episode schizophrenia. Given that psoriatic patients with cerebrovascular disease exhibit increased ORs for schizophrenia, it might be possible that disruption of the blood–brain barrier in psoriatic patients would activate the Th17 pathway in the brain, thereby potentiating susceptibility to schizophrenia. This possibility also explains why only psoriatic patients > 40-years old, who exhibit higher risks of cerebrovascular disease, have a higher prevalence of schizophrenia as compared with the comparison group. Further investigations are required to verify this hypothesis. The reason that psoriatic patients with chronic pulmonary disease exhibit increased ORs relative to those without chronic pulmonary disease remains to be clarified. It is possible that psoriatic patients with comorbid lung disease have a dysregulated immune response that is involved in both psoriasis and schizophrenia. Additionally, methotrexate use may increase the risk of lung diseases. It is possible that psoriatic patients with chronic pulmonary disease reflected those with severe psoriasis and receiving methotrexate treatment. Whether methotrexate use in psoriatic patients is associated with the higher prevalence is unclear. Further study is needed to elucidate potential associations between methotrexate use, psoriasis, and schizophrenia.