Atopic dermatitis (AD), the most common type of eczema, and inflammatory bowel disease (IBD), which includes conditions like Crohn’s disease (CD) and ulcerative colitis (UC), are two prevalent chronic health issues that affect millions of people around the world.
AD, characterized by itchy and inflamed patches of skin, often begins in childhood but can persist into adulthood. Approximately 9.6 million children in the U.S. have AD, along with 16.5 million adults.
CD and UC are the two main types of IBD. Although the exact cause of IBD is unknown, it is believed to involve an abnormal immune response in genetically susceptible individuals. According to information from the Centers for Disease Control and Prevention (CDC), an estimated 3.1 million adults in the U.S. have been diagnosed with IBD.
Both AD and IBD can have a significant impact on an individual’s quality of life. In addition to the physical discomfort and emotional distress they cause, they may also require ongoing medical management.
While these conditions are distinct from each other, studies have shown that there is a potential link between them. This has led clinicians and researchers to believe that understanding the prevalence, impact, and complex mechanisms of both AD and IBD is crucial to improving treatment options, providing appropriate care and support, and ultimately enhancing quality of life.
The Connection Between AD and IBD
Studies have shed light on a potential link between AD and IBD, the most recent of which was conducted by the Perelman School of Medicine at the University of Pennsylvania. It considered the risk of developing IBD in children and adults with AD, noting that data on the association between AD and IBD are inconsistent. This population-based cohort study included 409,431 children and 625,083 adults with AD. Results demonstrated a statistically significant increased risk of incident, or new-onset, IBD of 44% in children and 34% in adults compared with patients without AD.
The study also looked specifically at CD and UC for each group. Researchers found that children had an increased risk of CD, but only those with severe AD had an increased risk of UC. Adults, on the other hand, had an increased risk for both CD and UC. It was also noted that IBD risk increased with worsening AD severity.
Although previous studies have had mixed results, with some such as Weng et al. reporting that AD is not independently associated with IBD development, Alison Ehrlich, MD, MHS, a dermatologist at FoxHall Dermatology and Research Center in Washington, D.C. states, “While there does seem to be some inconsistencies in the association between IBD and AD, there are enough studies showing an association to state that the finding was not unexpected.”
A study published in October 2016 by Kim et al. examined the association between IBD and inflammatory skin diseases (ISDs). Their findings pointed to a significant association between IBD and ISD.
It is important to note that while these findings suggest a potential association between AD and IBD, more research is needed to fully understand the underlying mechanisms involved. Nonetheless, recognizing this connection could provide valuable insights for clinicians managing patients with either condition and potentially lead to improved treatment strategies for affected individuals.
Possible Shared Pathways Between AD and IBD
Although the exact nature of the relationship between AD and IBD continues to be explored, Joel M. Gelfand, MD, professor of dermatology and epidemiology at the University of Pennsylvania Perelman School of Medicine, and his team report, “The association between AD and IBD may be explained by shared genetic and environmental factors, immune cell activation, and alterations in skin and gut microbiota.”
Dr. Gelfand goes on to state that, “AD and IBD can cause changes in the microbiome, chronic inflammation, and the dysfunction in the skin and gut barrier respectively. There are also specific cytokines, certain kinds of proteins, that play a role in immune system activity and that seem to be related to AD and IBD. For example, we think dysfunction of types of T cells common to both AD and IBD, could be the culprits. Those need to be explored further to uncover both what’s happening at a microscopic level and what proteins or structures could be targeted to treat one or both conditions.”
According to Dr. Gelfand,
Treatment Implications for Patients with Coexisting AD and IBD
The authors of the most recent study note that “These findings provide new insights into the association between AD and IBD.” They add that “Clinicians should be aware of these risks, particularly when selecting systemic treatments for AD in patients who may have coincident gastrointestinal symptoms.”
Dr. Gelfand explains that dermatologists need to be aware of the immune-modulating treatments that can help treat both AD and IBD, such as upadacitinib. This second-generation selective Janus kinase (JAK) inhibitor is approved by the U.S. Food and Drug Administration to treat moderate to severe UC, moderate to severe CD, and moderate to severe AD.
In one study, a team of researchers demonstrated the case of a 36-year-old male suffering from both AD and UC who was treated with low-dose upadacitinib. Their successful use of the JAK inhibitor in this case led them to conclude that “upadacitinib may be the most suitable management strategy among subjects with coexisting severe conditions mediated by Th1 inflammation, such as UC, and by Th2 cytokines, such as AD.”
The Need for Further Research into the Link Between AD and IBD
While epidemiologic data demonstrates increased IBD susceptibility in those with AD, many questions remain unanswered about this intersection of inflammatory diseases. Further research is critical to delineate the genetic and immunologic mechanisms driving this association. Researchers explain that their study findings may help to demonstrate that IBD, CD, and UC risk increases with worsening AD severity, but they note that there is a need for more studies involving more diverse populations.
Studies to help illuminate biological pathways and define predictive metrics can equip clinicians to provide integrated care customized to a patient’s risk profile.
We have only begun scratching the surface of the intricacies connecting skin and gut. An expanded study of the AD and IBD relationship represents an exciting new frontier with immense clinical potential.