Erythema nodosum as a marker for objective disease activity in inflammatory bowel disease.

Background: Erythema nodosum (EN) is an inflammatory condition marked by tender, red nodules, typically on the extensor limbs. Though often linked to IBD activity, its association with objective markers like inflammatory labs or endoscopic findings remains unclear. This study examined the relationship between EN and objective inflammation in IBD patients. Methods: At a tertiary clinic with over 6500 patients, individuals with active EN were identified. Patients with active EN were identified, and symptomatic disease activity was assessed. Objective assessments included endoscopy, cross-sectional imaging (CT/MRI), fecal calprotectin, and CRP. Descriptive statistics compared objective and subjective disease activity in relation to EN. Results: Of 169 patients with documented EN, 95 had at least one objective assessment within our timeframe and were included. The mean age at EN presentation was 32 years; most had Crohn's disease (80%) and were female (75%). Among CD patients, 93% had colonic involvement and 32% had penetrating disease. A total of 77 (74%) patients had gastrointestinal symptoms at the time of EN presentation, and 84 (81%) had objective evidence of active disease. Endoscopy was performed in 66% of cases, with 58 patients (84%) showing active inflammation. Among CD patients, 53% had mucosal ulcerations, while 67% of UC patients had severe disease (Mayo E3). Conclusions: In this cohort, most patients presenting with EN had both symptomatic and objective signs of intestinal inflammation. These findings support the use of objective testing in IBD patients with EN and suggest EN may indicate a more severe or complicated disease course.