Psoriasis: An inflammatory skin disease affecting the mind

Psoriasis is a relatively common chronic inflammatory skin disorder affecting around 1%–2% of the global population. Its systemic manifestation has been widely underlined in recent years. The growing body of literature exploring the connection between psoriasis and extracutaneous systems contributes to a shift from recognizing psoriasis as a skin disease to an enhanced comprehension of an auto-inflammatory condition characterized by systemic inflammation. Apart from the well-studied diseases affecting cardiovascular, gastrointestinal or renal systems, many of us have expanded their attention to encompass the correlation between psoriasis and other systemic diseases, such as those affecting the mind. The growing attentiveness to the mental health problems is caused not only by the adverse impact of skin lesions on patients' well-being, but also as shared immune-mediated, inflammatory mechanism has been identified in those two systemic conditions.1 Yi et al.2 explored alterations in brain activity and impaired cognitive functions of a large cohort of 222 patients suffering from psoriasis in comparison to 144 age- and gender-matched healthy controls (HCs). To understand the above-mentioned alterations, each subject underwent thorough neuropsychological testing with multiple cognitive performance questionnaires, as well as brain resting-state functional magnetic resonance imaging (rs-fMRI). The results of the study clearly show that patients with psoriasis have lower cognitive function in comparison to HCs assessed with the Trail Making Test, Digit Span Test and Stroop Color-Word Test (p < 0.005 for all questionnaires). Moreover, rs-fMRI showed a decreased amplitude of low-frequency fluctuation (ALFF) in the left superior frontal gyrus, the left medial superior frontal gyrus and the right precuneus gyrus, which are all implicated in multiple cognitive processes, including, among others, motor planning, decision-making and reasoning. Interestingly, these aberrations are in accordance with the findings in patients with bipolar disorder. The changes in the rs-fMRI were significantly correlated with the patients' decrease in cognitive functions. The authors did not report a significant correlation between psoriasis severity assessed with the PASI scale and the ALFF value, yet it correlated positively with cognitive testing scores for attention, response inhibition, processing speed and memory. No difference was found in ALFF values and quality of life, depression and anxiety. The implications of psoriasis on patients' mental health have been vastly studied across the globe. It has been proven that regardless of patients' cultural background, psoriasis impairs quality of life and increases the prevalence of anxiety and depression, which often leads to suicidal ideations.3 Firstly, the influence of mental health affectation was believed to be mainly caused by the associated itch, as well as the visibility of skin lesions, shame and social stigmatization.3 Yet, it has been recently proven that the pathogenesis of psoriasis shares inflammatory pathways with different psychiatric disorders, including depression, anxiety, posttraumatic stress disorder (PTSD), schizophrenia and bipolar disorders.4 The complex inflammatory cycle of psoriasis is mainly driven by Th1/Th17 lymphocytes and proinflammatory cytokines, including, among others, IL-6, IL-17 and TNF α. Increased concentrations of similar cytokines have been observed in patients with depression, anxiety and schizophrenia.4 The overactivation of hypothalamic–pituitary–adrenal (HPA), observed in patients with psoriasis, has also been reported in patients with anxiety and PTSD.4 One should also underline that the increased concentration of TNF α may result in neuronal destruction or neurotoxic release of glutamate. Moreover, it has been found that TNF α, alongside IL-17, is implicated in the pathophysiology of systemic sclerosis, Alzheimer's disease and Parkinson's disease.5 In conclusion, the associations between psoriasis and mental health still remain unsolved; nevertheless, we are constantly widening our knowledge of these complex interactions. It is crucial to underline that the study by Yi et al.2 is one of the few studies assessing the functional changes in the central nervous system in psoriatic patients. Such results are tangible evidence of the influence of systemic inflammation associated with psoriasis on patients' mental health. No funding received. The authors declare no conflicts of interest. Data sharing is not applicable to this article as no new data were created or analyzed in this study.