GIT J Club ileal vs colonic CD

1. Kurdistan Board GEH/GIT Surgery J Club 2022
Supervised by Professor Dr. Mohamed Alshekhani.

2. Introduction:
 CD can affect any part of GIT.
 Current guidelines do not differentiate between small-intestinal &colonic
CD for medical treatment.
 Ileal CD is distinct from colonic CD in several intestinal layers:
 Colonic CD shows an overlap with regard to disease behaviour with UC,
underlining the fact that there is more to IBD than just CD/UC&subtypes,
possibly defined by location& shared pathophysiology.
 There are differences between Ileal&colonic CD using in epidemiology,
genetics, macroscopic differences(creeping fat), histological findings&
intestinal barrier including gut microbiota, mucus layer, epithelial cells &
infiltrating immune cell populations.
 These differences translate into the clinic, emphasizing the important role
of treatment decisions.

4.  Site-specific changes of the mesentery in Crohn’s disease.
 A.the mesentery under healthy conditions, adipocytes,
mesenchymal cells& immune cells are present. No significant
differences can be seen between the mesentery adjacent to the
ileum& thatadjacent to the colon.
 B. In Crohn’s disease, the mesentery of the ileum develops
characteristic changes including hyperplasia of adipocytes,
wrapping of the inflamed intestinal segment (creeping fat), fibrosis
&a strong immune cell infiltrate. In creeping fat, tertiary lymphoid
organs (TLOs) are found in close proximity to the lymphatic vessel
& B cells/ innate lymphoid cells invade the lymphatic wall.
 The mesentery of the inflamed colon is only loosely attached, the
adipocytes are of normal size& the immune cell infiltrate is only
mildly developed. The mesentery of the colon in Crohn’s disease
resembles the mesentery in ulcerative colitis.

6.  Site-specific changes in CD.
 A. Structural&immunological differences bet ileum& colon in a
healthy state.The ileum has single mucus layer partially penetrable
by intestinal microbiota,presents the first line of defence &contains
antimicrobial peptides (AMP)/IgA to defend translocalizing
bacteria.AMP produced by Paneth cells at the crypt.
 By contrast, healthy colon is characterized by a double layer of
mucus, where microbiota can penetrate the luminal layer but not
layer underneath,also contains AMP for defence,by secretory cells.
 B.Site-specific changes in CD, showing a decrease in the mucus
layer& composition, decreased diversity of gut microbiota/ AMP, a
disrupted epithelial barrier & the dominance of T helper 1(TH1)&
TH17 cells in the lamina propria of the terminal ileum.
 In colon, the two mucus layers equally decrease& change their
composition,the diversity of the microbiota changes in a site-
specific manner, epithelial cells are partially disrupted& a TH1
response dominates the lamina propria.

15. Conclusion:
 The principle differences between SI& colon,make it obvious that there are
site-specific changes in ileal& colonic CD.
 CD phenotype can be divided into 30% ileal disease, 40% ileocolonic
disease& 30% colonic disease
 Some suggested a new classification consisting of ileum-dominant& colon-
dominant disease.
 Even in isolated colonic dis, distinct changes of ileal microbiota are presen
&although inflammation is driven by different pathways, both sites seem
to influence each other.
 There is trend towards lower efficacy of biological therapies in isolated
ileal Crohn’s disease than in colonic.