Background: Inflammatory bowel disease (IBD) is a chronic, immune-mediated inflammatory disorder of the gastrointestinal tract. In IBD, systemic inflammation and immune dysregulation may also impact extraintestinal organs, such as the thyroid gland. Despite this, little is known about the influence of concomitant hypothyroidism on the clinical course of IBD.

Methods: A retrospective analysis was conducted among adult patients with IBD and at least one thyroid stimulating hormone (TSH) measurement within a large healthcare network. Patient charts were reviewed, and baseline demographics, disease characteristics, biomarkers, healthcare utilization, medication use, and other comorbidities were extracted. Patients were stratified by those with IBD only and those with concomitant IBD and hypothyroidism. Multivariable logistic regression was used to identify factors associated with concomitant hypothyroidism. Concomitant disease as an independent predictor for lab abnormalities and increased healthcare utilization was also assessed using multivariable logistic and negative binomial regression.

Results: We identified 287 adult patients with IBD, including 146 (50.9%) with Crohn's disease (CD) and 141 (49.1%) with ulcerative colitis (UC). Among this sample, 178 (62.0%) patients had concomitant hypothyroidism. Concomitant disease was associated with older age (adjOR 1.04, 95% CI 1.02, 1.06), female sex (adjOR 1.78, 95% CI 1.01, 3.16), and the presence of other extraintestinal manifestations (adjOR 2.30, 95% CI 1.06, 5.00). Concomitant disease was also found to be a significant predictor for increased healthcare utilization, specifically, higher number of radiation-based abdominal imaging (RBAI) studies (adjIRR: 1.89, 95% CI 1.08, 3.32).

Conclusions: Patients with both IBD and hypothyroidism have an increased likelihood of other extraintestinal manifestations compared to individuals who have IBD without hypothyroidism. Furthermore, patients with concomitant disease exhibited greater healthcare utilization, specifically, increased rates of RBAI studies. The presence of concomitant hypothyroidism may be associated with a more severe course of IBD.