Does Psoriasis Cause IBD?
Psoriasis does not directly cause IBD, but patients with psoriasis have a significantly increased risk of developing inflammatory bowel disease—approximately 2.5 times higher risk for Crohn's disease and 1.7 times higher risk for ulcerative colitis compared to the general population. 1, 2
Understanding the Association
The relationship between psoriasis and IBD represents a bidirectional association rather than direct causation. These conditions share common pathophysiologic mechanisms including:
- Shared genetic susceptibility loci and immune dysregulation, particularly involving the IL-23/IL-17 axis and TNF-α signaling pathways 3, 4
- Common inflammatory pathways involving dendritic cells, Th17 cells, and increased epithelial barrier permeability in both skin and intestinal mucosa 3
- Overlapping immune-mediated mechanisms that explain why both conditions frequently coexist within the same patient or family 1, 3
Quantifying the Risk
The epidemiologic data demonstrates clear increased prevalence:
- Crohn's disease prevalence ratio: 2.49 in psoriasis patients versus controls 1
- Ulcerative colitis prevalence ratio: 1.64-1.91 in psoriasis patients versus controls 1, 5
- Meta-analysis confirms psoriasis patients have increased odds of Crohn's disease (OR 1.70) and ulcerative colitis (OR 1.75), with increased risk ratios of 2.53 and 1.71 respectively 2
Patients with psoriatic arthritis, particularly those with axial disease, demonstrate even higher incidence and prevalence of IBD compared to those with psoriasis alone 1
Clinical Screening Imperatives
Screen all psoriasis patients for IBD symptoms before initiating systemic therapy and monitor throughout treatment. 5 Red flag symptoms requiring immediate gastroenterology referral include:
- Chronic diarrhea lasting ≥3 months 1
- Nocturnal bowel symptoms causing awakening from sleep 1
- Non-hemorrhoidal rectal bleeding 1
- Chronic abdominal pain 1
- Perianal fistula or abscess 1
- Unintentional weight loss 1
Critical Treatment Considerations
When treating patients with both conditions:
- TNF inhibitors (adalimumab, infliximab) or ustekinumab (IL-12/23 inhibitor) are preferred as they effectively treat both psoriasis and IBD 5, 6
- Strictly avoid IL-17 inhibitors (secukinumab, brodalumab, ixekizumab) in patients with known or suspected IBD, as these agents exacerbate Crohn's disease in clinical trials 1, 5, 6
- Methotrexate shows efficacy for both conditions and can be used in combination with biologics 1
Common Pitfall to Avoid
The most dangerous error is prescribing IL-17 inhibitors to psoriasis patients without first screening for IBD symptoms. These medications can trigger or severely worsen inflammatory bowel disease, even in patients without prior IBD diagnosis 1, 6. Always obtain a thorough gastrointestinal history before initiating any systemic psoriasis therapy.