Editing Crohn's disease (section)

== '''Workup''' ==

* No single diagnostic test for CD - multimodal approach
* '''Bloods'''
** FBE - check for anaemia and thrombocytopaenia
** UEC
** LFT (PSC screen)
** Iron and other nutritional deficiencies
** CRP < 5 has a >99% sensitivity for active IBD.
** Serologic markers
*** Antibodies against Saccharomyces cerevisiae (ASCA) - positive in 35-50% of Crohn's, and <1% of UC
*** Perinuclear antineutrophilic cytoplasmic antibodies (p-ANCA)
**** (Helpful in differentiating Crohn's and UC - ASCA positive, p-ANCA negative suggests CD, whereas p-ANCA is more likely to be elevated in UC)
*** Coeliac antibodies
*** QuantiFERON gold if considering immunologics
* '''Stool studies'''
** '''MCS''' (rule out infectious causes)
** '''Faecal calprotectin'''
*** Non-specific, but helpful screening tool
*** In general, more elevated in large bowel than small bowel, but often up in both
*** Patients can have quite variable degrees of elevation with their disease, so it's more useful as a marker over time for each patient than as an absolute comparator between patients
*** FC <50mcg/g - sensitivity approaching 100% for colitis
*** FC <50-100 mcg/g = likely quiescent disease
*** FC > 250mcg/g = likely inflammation
** '''Faecal lactoferrin'''
*** >6ng/mL predicts small bowel inflammation at a similar accuracy to calprotectin
* '''Endoscopy'''
** Gold standard for diagnosis
** Aim for at least two biopsies from five sites, with TI intubation
** Strictures should be biopsied (24% risk of malignancy in UC and 6% in CD)
** Expect patchy segmental inflammation
*** Longitudinal ulcers
*** In early CD, plenty of normal mucosa - cobblestone appearance
*** In later CD, hard to differentiate UC from CD due to extensive disease
***

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* Double-balloon enteroscopy allows increased enteral intubation than push enteroscopy or ileocolonoscopy
* Use CD index of severity or Simple Endoscopic Score (below) to quantify disease
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* Score decrease of 50% in SES-CD at week 26 correlates with steroid-free remission at week 50

* '''Capsule endoscopy'''
** Only indicated if imaging has shown small-bowel disease, but it is inaccessible to traditional endoscopy
** Careful use - capsule retention (for longer than 2 weeks) is much higher in CD patients than general population (13% vs 2%)
** 3 or more ulcers in the absence of NSAID use is considered abnormal
** Severity measured using the Capsule Endoscopy Crohn Disease Activity Index
* '''Imaging:'''
** MRE (sens 86% spec 93%) / CTE (sens 87% spec 91%) for small bowel inflammation in CD
*** MRE is better than CT in detecting intestinal strictures and ileal wall enhancement, and fistulas and sinus tracts
*** Need to drink 1.5-2L of fluid in the hour prior
** MRI better for perianal disease
** CT enterography
*** Mucosal irregularity and hyperdensity
*** Stenosis
*** Prestenotic dilation
*** Mesenteric hypervascularity (comb sign)
** CT abdo/pelvis
*** Most useful to identify acute complications
** USS
*** Somewhat useful for detecting TI disease, but very inaccurate for disease proximal to TI
* '''Operative findings'''
** Abdominal
*** Thickened grey-pink or dull purple-red loops of bowel, with areas of thick grey-white exudate or fibrosis of the serosa
*** Involved segments often adherent to adjacent loops or other viscera, possibly with internal fistulas
*** Thickened mesentery with enlarged lymph nodes
*** Skip areas of healthy bowel
**** Uninvolved bowel may be dilated secondary to distal obstruction
*** Fat wrapping (also known as creeping fat) - circumferential growth of the mesenteric fat around the bowel wall
*** Bowel becomes thickened, firm, rubbery and difficult to compress as the disease progresses
***
** Bowel mucosa
*** Earliest lesions are superficial aphthous ulcers in the mucosa
*** Ulceration becomes more pronounced over time - characteristically linear
*** Cobblestone appearance - transverse sinuses with islands of normal mucosa in between
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