Depression as a risk factor for the development of psoriasis: a retrospective cohort study in the United Kingdom.

: Psoriasis is a chronic systemic disease with characteristic papules, plaques and nail changes distributed in highly visible locations. This may contribute to the increased prevalence of depression observed in psoriasis patients compared to the general population.1,2 Interestingly, people with depression without systemic inflammatory disorders have increased levels of inflammatory cytokines including tumor necrosis factor-alpha and Interleukin-6,3 as is seen in psoriasis,4 thereby suggesting a potential for a shared inflammatory pathway. Recent evidence supports a link between depression and the subsequent development of other immune-mediated disease.5-7 As depression has been demonstrated to have an influence on the disease course of psoriasis and increase the risk of psoriatic arthritis,5 we hypothesize that depression may also confer a heightened risk of developing psoriasis.