Psoriasis and Inflammatory Bowel Disease: Two Sides of the Same Coin?

Abstract

Crohn’s disease (CD) and ulcerative colitis (UC) are inflammatory bowel diseases (IBDs) that share common pathogenesis and clinical behaviour.¹ Both innate and adaptive immunity appear to play a key role in triggering and maintaining chronic inflammation in IBD. The involvement of both these arms of the immune system is common to other immune-mediated diseases (IMIDs), such as rheumatoid arthritis, ankylosing spondylitis and psoriasis, hence the use of similar therapeutic strategies, including the use of steroids, immunomodulators and monoclonal antibodies in all these diseases.² In particular, psoriasis can be associated with IBD as an independent concomitant IMID, or can be a manifestation of underlying IBD, or even a paradoxical adverse event of anti-tumour necrosis factor (TNF) therapy.^3,4 Such an association could be related to shared genetic abnormalities, common cytokine-driven inflammation [such as the interleukin 23 (IL-23) and Th17 pathway] or environmental factors. However, the link between psoriasis and IBD is currently far from clear. It is known that psoriasis is observed at a frequency about eight times higher among patients with CD than in the general population.⁵