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Crohn’s disease: inflammatory type
Abbreviations
Crohn’s disease gastrointestinal inflammatory bowel disease ileocecal valve intestinal tuberculosis primary sclerosing cholangitis ulcerative colitis CD
GI
IBD
ICV
ITB
PSC
UC
Introduction
Crohn’s disease (CD), by location, can involve any part of gastrointestinal (GI) tract, from the mouth to anus. CD can also involve the GI tract with different depths. Therefore several classifications have been proposed to categorize CD. The Montreal classification was proposed to categorize CD, on the basis of the age of onset, disease location, and disease phenotype ( Table 4.1 ), which was modified from earlier Vienna classification . The classifications were recently further expanded by the incorporation of age groups, disease locations, and etiopathogenetic factors ( Table 4.2 ).
Table 4.1
The Montreal classification of Crohn’s disease .
| Age at diagnosis (A) | ||
| A1 16 years or younger | ||
| A2 17–40 years | ||
| A3 over 40 years | ||
| Location (L) | Upper GI modifier (L4) | |
| L1 terminal ileum | L1+L4 | Terminal ileum +upper GI |
| L2 colon | L2+L4 | Colon+upper GI |
| L3 ileocolon | L3+L4 | Ileocolon+upper GI |
| L4 upper GI | – | – |
| Behavior (B) | Perianal disease modifier (p) | |
| B1 nonstricturing, nonpenetrating | B1p | Nonstricturing, nonpenetrating+perianal |
| B2 stricturing | B2p | Stricturing+perianal |
| B3 penetrating | B3p | Penetrating+perianal |
A , Age; B , behavior; GI , gastrointestinal; L , location.
Table 4.2
Proposed classification of inflammatory bowel diseases.
| Criteria | Class | Description | Examples | |
|---|---|---|---|---|
| Disease location, extent and depth ± granulomas | Ulcerative colitis | Classic UC | ||
| Crohn’s disease | Classic CD | |||
| Indeterminate colitis | ||||
| Age of onset | Very early onset | Age 0 | IL-10/ILR mutations | |
| Early onset | Age 0–10 years | |||
| Age 10–17 years | ||||
| Regular onset | Age 17–40 years | |||
| Late onset | Age >50 years | |||
| Phenotype | Inflammatory | Inflammatory CD; classic UC | ||
| Stricturing | Stricturing CD; UC with stricture | |||
| Penetrating | Fistulizing CD | |||
| Locations | Oral | |||
| Upper GI | ||||
| Jejunum | ||||
| Ileum | ||||
| Colon | ||||
| Rectum | ||||
| Perianal | ||||
| Extraintestinal | Metastatic CD of the skin, lung, and liver | |||
| Concurrent or immune-mediated disorders | IBD | Isolated UC or CD of the gut | ||
| IBD-V | IBD + | IBD+classic extraintestinal manifestations | UC with concurrent PSC | |
| IBD ++ | IBD+autoimmune and/or autoinflammatory disorders±classic extraintestinal manifestations | IBD with concurrent microscopic colitis, celiac disease, hidradenitis suppurativa | ||
| IBD +/− | Diseases sharing clinical features and possible etiopathogenetic pathways with classic IBD ± classic extraintestinal manifestations of IBD, autoimmune disorders or autoinflammatory disorders | Lymphocytic colitis, collagenous colitis; Behcet disease, cryptogenic multifocal ulcerous stenosing enteritis, ulcerative jejunitis | ||
| Etiology of IBD | Primary or idiopathic | Monogenic | IL-10, IL-10Ra, IL-10Rb mutations | |
| Very early–onset IBD | ||||
| Polygenic | Classic UC; classic CD | |||
| Secondary | Identifiable pathogens | Mycobacterial paratuberculosis | ||
| Medication-induced | Mycophenolate-associated colitis; ipilimumab-associated colitis | |||
| Organ transplantation-induced | Post–solid organ transplant IBD-like conditions, cord colitis syndrome | |||
| Surgery induced | Pouchitis, Crohn’s disease–like conditions of the pouch, post–colectomy enteritis, bariatric surgery–associated IBD | |||
| Genetic etiology | Monogenic | IL-10/IL-R mutations, familial Mediterranean fever | ||
| Polygenic | Classic CD and classic UC | |||
| Disease spread process | Intrinsic (inside-out) | Starting from the lymphatic system or mesentery, spreading to gut mucosa | Subset of obese CD patients; subset of sclerosing mesenteritis or lymphangitis | |
| Extrinsic (outside-in) | External trigger (e.g., bacteria) leading to mucosal inflammation | Fulminant UC: from mucosal disease to transmural inflammation | ||
CD , Crohn’s disease; IBD , inflammatory bowel disease; IBD-V , IBD-variant; PSC , primary sclerosing cholangitis; UC , ulcerative colitis.
This chapter is focused on inflammatory phenotype of CD. Fibrostenotic ( Chapter 5 : Crohn’s disease: fibrostenotic type), fistulizing ( Chapter 6 : Crohn’s disease: penetrating type), and perianal ( Chapter 7 : Crohn’s disease-perianal) phenotypes are discussed in separate chapters.
Esophagogastroduodenoscopy and ileocolonoscopy play a key role in the evaluation, diagnosis, differential diagnosis, disease monitoring, and assessment of treatment response of CD ( Table 4.2 ).
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