Psoriasis and comorbidities. Epidemiological studies.

Psoriasis is a prevalent chronic inflammatory disease whose exact aetiology is not fully understood, but both genetic and environmental factors have been implicated in the onset and progression of the disease. At the skin level, psoriasis is characterized by localized or widespread thick raised silvery-white scaling and pruritic plaques and studies have shown that psoriasis negatively affects patients' quality of life, and depression occurs more often in patients with psoriasis. However, data have shown that psoriasis is a systemic disease which affects the joints, vasculature, and other tissues as well. Indeed, approximately one-third of patients with psoriasis develop psoriatic arthritis, and patients with severe psoriasis have a shortened life expectancy. Although our knowledge of the pathogenesis of psoriasis has advanced significantly in the past decade, as have the pharmacological treatment options which are now available, several important knowledge gaps remain. Many of the proinflammatory mediators involved in psoriasis have also been implicated in some central nervous system (CNS) diseases. However, studies on associations between psoriasis and CNS diseases are scarce. Based on nationwide registry data from the entire Danish population, the present thesis examined the associations between psoriasis and certain CNS diseases. The specific objectives of this work were to investigate the independent impact of depression on the risk of cardiovascular disease (CVD) in patients with psoriasis, the relationship between psoriasis and uveitis, and the risk of incident multiple sclerosis (MS) following the onset of psoriasis, respectively. The main results were a significantly increased risk of myocardial infarction, stroke, and CVD death in patients with psoriasis during stages of acute depression. Moreover, we found a bidirectional relationship between psoriasis and uveitis, where the occurrence of either disease significantly increased the risk of the other. Perhaps most notably, however, was that we found a psoriasis-severity dependent increased risk of MS. In conclusion, psoriasis was significantly associated with certain CNS diseases, and the risk of CVD was strongly associated with acute depression in these patients. These novel findings suggest an important link between psoriasis and CNS diseases, and high-light the necessity for a holistic approach to the diagnosis and treatment of patients with psoriasis.