Background: The Inception Cohort Registry Study of Patients with Crohn’s Disease aimed to clarify clinical characteristics and disease course of newly diagnosed Crohn’s disease patients in Japan throughout a 4-year period. Results from an interim analysis of the largest nation-wide registry study that covers approximately 1% of Crohn’s disease patient population in Japan are reported. Methods: This prospective, observational registry study was conducted at 19 tertiary centers in Japan. Patients newly diagnosed with Crohn’s disease after June 2016 (age ≥ 16 years at informed consent) were enrolled between December 17, 2018 and June 30, 2020. Patient demographics, diagnostic procedures and categories, disease location and lesion behavior (Montreal classification) at the time of diagnosis were recorded. Results: Of 673 patients enrolled, 672 (99.9%) were analyzed (458: men, 214: women), male-to-female ratio: 2.1, median age at diagnosis 25 (range 13–86) years; peak age of disease diagnosis: 20–24 years. Most common disease location was L3 (ileocolonic; 60.1%). Non-stricturing, non-penetrating (B1) disease was most common behavior (62.8%); 48.9% reported perianal lesions. Notably, age-wise analysis revealed disease phenotypes varied between patients aged < 40 and ≥ 40 years in terms of male-to-female ratio (2.5/1.3)/disease location (L3: 66.3%/37.0%)/disease behavior (B1: 66.4%/50.0%)/perianal lesion: (55.7%/20.5%) at Crohn’s disease diagnosis, respectively. Conclusions: Interim analysis of this nation-wide Inception Cohort Registry Study of Patients with Crohn’s Disease revealed the demographics and disease characteristics of newly diagnosed Crohn’s disease patients in Japan and demonstrated that disease phenotype varied between patients aged < 40 and ≥ 40 years, serving as important information for management of individual patients.
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