As patients’ atopic dermatitis (AD) worsens, the risk of inflammatory bowel disease, Crohn disease, and ulcerative colitis increases.
Although previous studies analyzed the relationship between AD and IBD, the researchers noted that the data are inconsistent. Additionally, few studies separately examined the association of AD with the risk of ulcerative colitis (UC) and CD. Because of this, they conducted a study to analyze the risk of new-onset IBD, UC, and CD in children and adults with AD.
The researchers created their study population of children and adults using data recorded between January 1, 1994, and February 28, 2015, in The Health Improvement Network (THIN), an electronic health records database comprised of patients registered with UK general practices; THIN is thought to be representative of the general UK population.
They considered patients to have AD if they had at least 1 of 5 diagnostic codes for it and 2 AD-related treatment codes. The researchers put those with AD under the age of 18 into the pediatric cohort and those over the age of 18 into the adult cohort.
Because THIN does not capture AD severity, treatment exposure was used as a proxy. By default, the researchers classified all patients' AD as mild. They worsened the classification to moderate AD when either “the second potent topical corticosteroid prescription within 1 year or the first topical calcineurin inhibitor prescription.”
Also, the researchers classified patients as having severe AD “at first systemic immunosuppressant prescription, any prescription for phototherapy, or dermatologic referral because most patients with AD are treated by their general practitioner.” Throughout the study, the researchers recorded when patients' AD worsened, but they did not change the classification if someone's AD improved.
In the pediatric population, the researchers matched a total of 1,809,029 controls to 409,431 children with AD. Of those with AD, 93.2% of cases were classified as mild, 5.5% as moderate, and 1.3% as severe. Additionally, the population ranged in median age from 4 to 5 years (overall range, 1-10 years).
The researchers found that children with AD had a 44% increased risk of IBD (HR, 1.44; 95% CI, 1.31-1.58) and a 74% increased risk of CD (HR, 1.74; 95% CI, 1.54-1.97), which increased as AD worsened. On the other hand, most children with AD did not have an increased risk of UC (HR, 1.09; 95% CI, 0.94-1.27) besides those with severe AD (HR, 1.65; 95% CI, 1.02-2.67).
As for the adult population, it was composed of 2,678,888 controls and 625,083 patients with AD. Of those with AD, 65.7% were classified as having mild AD, 31.4% were classified as having moderate AD, and 2.9% were classified as having severe AD. The adult population ranged in median age from 45 to 50 years (overall range, 30-68 years).
Adults with AD had a 34% (HR, 1.34; 95% CI, 1.27-1.40) increased risk of IBD, a 36% (HR, 1.36; 95% CI, 1.26-1.47) increased risk of CB, and a 32% (HR, 1.32; 95% CI, 1.24-1.41) increased risk of UC. As patients' AD worsened, the risk increased across all 3 disease states.
“These findings provide new insights into the association between AD and IBD,” the authors wrote. “Clinicians should be aware of these risks, particularly when selecting systemic treatments for AD in patients who may have coincident gastrointestinal symptoms.”
The researchers acknowledged that their study had several limitations, one being that they used treatments to represent severity, which made it difficult to separate the effects of treatment exposure from those of AD severity. Also, the researchers noted that they treated AD severity as a time-updated variable. This allowed for escalation of severity but not de-escalation, meaning severe AD was not reclassified as moderate, even if AD improved.
Despite these limitations, the researchers explained that their study findings helped to demonstrate that IBD, CD, and UC risk increases with worsening AD severity, suggesting a possible causal association. As for future research, they noted the need for studies involving more diverse populations “to help substantiate the validity” of their findings.
Chiesa Fuxench ZC, Wan J, Wang S, et al. Risk of inflammatory bowel disease in patients with atopic dermatitis. JAMA Dermatol. Published online August 30, 2023. doi:10.1001/jamadermatol.2023.2875