Crohn disease
Summary
Crohn disease (CD) is an inflammatory bowel disease (IBD), the pathogenesis of which is not fully understood. The clinical presentation of CD may be similar
to ulcerative colitis (UC), the other most common IBD. CD mostly affects young adults and adolescents between the ages of 15 and 35. It typically affects the
terminal ileum, but can discontinuously affect the entire gastrointestinal tract and commonly leads to complications such as fistulas, abscesses, and stenosis.
Clinical features include diarrhea, weight loss, and abdominal pain in the right lower quadrant (RLQ), as well as extraintestinal manifestations in the
eyes, joints, or skin. Diagnosis is based on the patient's medical history, physical examination, lab tests, imaging (e.g., MRI), endoscopy, and serological
testing. Acute episodes are treated with corticosteroids; immunosuppressants may be indicated in severe cases. Antibiotics and surgical intervention may be
needed to help treat complications. As Crohn disease is not localized to a specific region of the GI tract, surgical resection is not a curative option (unlike in
UC), and treatment instead focuses on limiting the progression and recurrence of inflammatory episodes.
NOTES
FEEDBACK
Epidemiology
 Prevalence: 200 cases per 100,000 population
 Incidence: ∼ 6 cases per 100,000 population per year [1]
 Sex: ♂ = ♀
 Typical age of onset: bimodal distribution with one peak at 15–35 years and another one at 55–70 years [2][3]
 Populations with higher prevalence [4]
o Individuals of Northern European descent
o Individuals of Ashkenazi Jewish descent
Epidemiological data refers to the US, unless otherwise specified.
NOTES
FEEDBACK
Etiology
 Cause: Immune dysregulation and dysbiosis, which promotes chronic inflammation, the ultimate cause of which is not fully understood.
 Risk factors [4]
o Active and passive smoking of tobacco
o Familial aggregation
o Genetic predisposition (e.g., mutation of the NOD2 gene, HLA-B27 association)
Nicotine consumption is the only (known) controllable risk factor for Crohn disease. Therefore, smoking cessation is especially important in patients with CD.
NOTES
FEEDBACK
Crohn disease activity index (CDAI)


Definition: A validated score used to assess disease activity in Crohn disease calculated using the following variables, assessed over the course of one
week:
o Number of liquid or soft stools per day
o Severity of abdominal pain
o General condition
o Presence of the following
 Arthritis/arthralgia
 Iritis/uveitis
 Erythema nodosum, pyoderma gangrenosum, or aphthous ulcers
 Anal fissures, fistulas, or abscesses
 Other fistulas
 Fever
o Use of antidiarrheal drugs
o Abdominal masses
o Hematocrit
o Percentage above or below standard weight
Interpretation
o 0–149: asymptomatic remission
o 150–220: low to moderate activity
o 221–450: moderate to high activity
o 451–1100: high activity, fulminant disease
NOTES
FEEDBACK
Pathophysiology
Inflammation
Inflammation is most likely caused by immune dysregulation.
 Dysregulation of IL-23-Th17 signaling → unrestrained Th17 cell function → inflammation → local tissue damage (edema, erosions/ulcers, necrosis)
→ obstruction, fibrotic scarring, stricture, and strangulation of the bowel [5]
 There is evidence that mutations in the nucleotide oligomerization binding domain 2 (NOD2) protein are involved in the development of Crohn
disease, but the exact mechanism is not fully understood. [5]
o Loss of function mutations in NOD2 → ↑ susceptibility for bacterial invasion of the intestinal mucosa → unregulated inflammation
o Dysfunctional NOD2 → overactivity of NF-κB signaling pathway → ↑ production of proinflammatory cytokines and
antimicrobial peptides → chronic autoinflammation
Abscess and fistula formation
Intestinal aphthous ulcers → transmural fissures and inflammation of the intestinal walls → adherence of other organs or the skin → penetration
→ microperforation and abscess formation → macroperforation into these structures → fistula formation
NOTES
FEEDBACK
Clinical features
CD typically occurs episodically with a 30%-risk of recurring inflammation over the span of one year. If symptoms persist for six months, the disease is
considered chronic. Without treatment, relapses and complications are to be expected.
Constitutional symptoms [6]
 Low-grade fever
 Weight loss
 Fatigue
Intestinal symptoms [6]
CD most commonly affects the terminal ileum and colon, but involvement of any part of the GI tract (from mouth to anus, except rectum) is possible.
 Chronic diarrhea, typically nonbloody
 Abdominal pain, typically in the RLQ
 Malabsorption (see “Signs of malabsorption” in “Complications” below)
 Palpable abdominal mass
in the RLQ


Enterocutaneous perianal fistulas, often associated with abscess formation [7]
Oral aphthae
Perianal fistulas and abscesses are often the first signs of Crohn disease.
Extraintestinal symptoms [8]
 Joints: enteropathic arthritis (e.g., sacroiliitis, spondylitis, inflammation of peripheral joints)
 Eyes
o Uveitis
o Iritis
o Episcleritis
 Liver/bile ducts: cholelithiasis


Urogenital system: urolithiasis (mostly calcium oxalate stones)
Skin
o Erythema nodosum
o Acrodermatitis enteropathica
o Pyoderma gangrenosum
 Associated with various conditions (e.g., IBD, rheumatoid arthritis, and trauma)
 Manifests with very painful, rapidly-progressive, red spots that can change into purulent pustules or deep ulcerated lesions with
central necrosis
 Commonly located at extensor side of the lower limbs
 Treated with immunosuppressants (e.g., corticosteroids, cyclosporine A)
o Pyostomatitis vegetans
NOTES
FEEDBACK
Diagnostics
Approach
Diagnosing CD requires the integration of clinical presentation, laboratory tests, and endoscopic, histologic, pathologic and radiologic findings.
1. If a patient presents with symptoms suggestive of CD, conduct blood tests and stool tests (see “Laboratory tests” below) to rule out other possible
causes for bowel inflammation/GI symptoms. [9]
2. Confirm diagnosis with endoscopy and/or radiographic imaging and/or biopsy.
3. Perform contrast radiological studies and/or ultrasonography to assess extent, severity, and complications (e.g., abscesses, fistulas, and stenoses)
Laboratory tests
Blood [9]
 Blood work
o Complete blood count may show signs of pernicious anemia
o ↑ Inflammatory markers (↑ CRP, ↑ ESR, ↑ thrombocytes, and ↑ leukocytes)
 Serology: routine use to establish diagnosis is not recommended due to low sensitivity
[10]
o
o
↑ Anti-Saccharomyces cerevisiae antibodies (ASCA)
pANCA most likely negative
Stool

Stool analysis
o Stool culture to rule out bacterial gastroenteritis
o Microscopy to examine presence of worm larvae or eggs (ova and parasites)
o Identification of bacterial toxins (e.g., toxin of Clostridium difficile)
o Detection of fecal calprotectin and/or fecal lactoferrin
[11][12]
Proteins associated with neutrophils that can be used as a diagnostic tool for inflammatory bowel disease
Direct correlation between detected amount of proteins and severity of intestinal inflammation
 Fecal occult blood test (FOBT)
Imaging [13][14]
 Plain x-ray abdomen: may show bowel distention or pneumoperitoneum
 Upper GI series with barium swallow and small bowel follow-through (enteroclysis):
used to detect fistulas or stenoses, characteristic findings are:
o Procedure
 Water-soluble contrast medium is inserted into the small intestine via a nasopharyngeal tube.
 Multiple x-rays are taken in a chronological sequence to evaluate each section.
o Findings
 String sign: contrast-filled bowel segment that resembles a string on x-ray


Creeping fat: pathognomonic hyperplasia of adipose tissue that results in accumulation of mesenteric fat around the circumference of
the intestine [15]
 May cover more than 50% of the inflamed bowel
 Correlates with severity of transmural inflammation
Ultrasound findings
o Gastrointestinal wall thickening caused by inflammation and edema
o Possible detection of abscesses/fistulas
MR enterography: noninvasive, highly sensitive and specific imaging technique that involves the visualization of an oral contrast medium on MRI and
is used in the diagnosis of IBD.
o Used to assess the extent and pattern of intestinal inflammation, detect perianal and pelvic disease, and to predict disease activity
o Characteristic findings are an edematous thickening of the intestinal wall and enlarged lymph nodes.
o Can be done as invasive MRI enteroclysis, during which contrast medium is applied via nasoduodenal tube and the small bowel is distended via
an electric infusion pump.



Endoscopy [16]
Endoscopy confirms the diagnosis, assesses the extent of the disease, differentiates CD from other diseases (e.g., ulcerative colitis, peptic ulcers, etc.), and
may also be used as a therapeutic tool (e.g., dilatation of ducts, intestinal loops).
 Ileocolonoscopy: endoscopic examination of the rectum, colon, and terminal ileum that allows for direct visualization of the intestinal mucosa and
sampling of tissue
o Procedure: ileocolonoscopy with biopsies at various locations throughout the terminal ileum, colon, and rectum
o Characteristic macroscopic findings
 Segmental/discontinuous pattern of involvement
 Snail trails: longitudinal ulcerations
 Pinpoint lesions: small, aphthous hemorrhagic mucosal defects
 Cobblestone sign: inflamed sections followed by deep ulcerations that resemble cobblestones
 Erythema and transmural inflammation (all mucosal layers of the intestinal wall are involved)
 Fissures, fistulas
 Esophagogastroduodenoscopy
o Used to evaluate for involvement of the esophagus, stomach, and duodenum
o Findings include aphthae on mucosa
 Video capsule endoscopy [13]
o Used to evaluate small bowel morphology as an adjunctive to regular endoscopy
o Should be performed prior to regular endoscopy in suspected small bowel obstruction
NOTES
FEEDBACK
Pathology
 Skip lesions: a pattern of patchy, discontinuous inflammation in the bowel (affected areas interspersed with normal tissue)
 Creeping fat


Hypertrophic lymph nodes
Transmural inflammation
o Noncaseating granulomas
[17]
o
o
Giant cells
Distinct lymphoid aggregates of the lamina propria
NOTES
FEEDBACK
Differential diagnoses
MAXIMIZE TABLETABLE QUIZ
Crohn disease and ulcerative colitis
Symptoms
Crohn disease
Ulcerative colitis
Pathophysiology

Mediated by dysfunctional IL-23-Th17 signaling

Mediated by Th2 cells
Frequency/type of
defecation



Increased
Typically nonbloody, watery diarrhea
May be bloody in more severe cases




Greatly increased
Bloody diarrhea with mucus
Tenesmus
Urgency

Nutritional status

Poor or malnourished
Mostly normal, but weight loss
and malnutrition may occur in severe disease


Painful defecation, pain located in LLQ
Abdominal cramps and tenderness
[18]
Physical
examination


Mostly constant pain in RLQ
Palpable abdominal mass
Crohn disease and ulcerative colitis
Symptoms
Extraintestinal
manifestations
Crohn disease
Ulcerative colitis

Low-grade fever


Nephrolithiasis (e.g., calcium oxalate)
Cholelithiasis

Skin
o
o


Tachycardia
Orthostatic hypotension

Primary sclerosing cholangitis
Pyoderma gangrenosum
Erythema nodosum

Eyes


Uveitis
Episcleritis
Mouth: aphthous stomatitis
Joints
o Peripheral arthritis
o Spondylitis
Fistulas


Common (to skin, bladder, or in between loops)
May cause pneumaturia and/or recurrent UTIs

Rare
Other
complications



Abscess
Strictures (obstructions)
Perianal fissures



Fulminant colitis
Toxic megacolon
Perforation


Increased due to underlying pathology
Increased secondary to immunosuppression



Small intestine
Colon
Non-Hodgkin lymphoma


Cholangiocarcinoma
Colorectal cancer
Cancer risk
o
o
[19]
Crohn disease and ulcerative colitis
Symptoms
Crohn disease
Ulcerative colitis

ASCA

p-ANCA


Colon (exception: backwash ileitis)

Typical location: terminal ileum and colon with rectal
sparing
May affect the entire GI tract
Pattern
of inflammation

Discontinuous (skip lesions)

Continuous
Typical diagnostic
findings





Cobblestone sign
Pinpoint lesions
Snail trails
Creeping fat
String sign




Friable mucosa
Mucosal ulcerations can be deep or superficial
Crypt abscesses
Loss of haustra (lead pipe sign)




Transmural inflammation
Noncaseating granulomas
Giant cells
Lymphoid aggregates


Confined to mucosa and submucosa
No granulomas

Neutrophilic inflammation of the crypts



Corticosteroids
Thiopurine analogs (azathioprine, 6-mercaptopurine)
Anti-p40 antibodies (e.g., ustekinumab)



5-aminosalicylic acid (e.g., mesalamine)
6-mercaptopurine
Calcineurin
inhibitors (e.g., cyclosporine, tacrolimus)
Antibodies
Endoscopy and imaging
Location
Histology
Treatment
Medication
Crohn disease and ulcerative colitis
Symptoms
Crohn disease


Surgery
Ulcerative colitis
Alpha 4 integrase inhibitors (e.g., natalizumab,
vedolizumab)
Possibly antibiotics outside of an acute episode
(e.g., ciprofloxacin, metronidazole)

Biologics (e.g., infliximab, adalimumab)

Noncurative surgery may become necessary to
alleviate symptoms

Curative surgery possible (proctocolectomy)
To remember the most important features of Crohn disease (creeping fat, granuloma, skip lesions, rectal sparing, cobblestone sign), think: The crone and
the fat granny skipped over the wrecked cobblestones.
Other differential diagnoses
 Acute appendicitis
 Infectious gastroenteritis/colitis
 Noninfectious colitis (ischemic, after radiation therapy, after ingestion of drugs, etc.)
 Diverticulitis
 Irritable bowel syndrome
 Gastrointestinal tuberculosis
 Malignant intestinal transformations
The differential diagnoses listed here are not exhaustive.
NOTES
FEEDBACK
Treatment
Approach [13]
 Therapy of CD is based on the following steps:
1. Treating acute disease
2. Inducing clinical remission
3. Maintaining response/remission
 Patients should be stratified according to their specific prognostic risk factors.
 For optimal results, therapy should be as individually tailored as possible.
 Disease activity should be monitored regularly based on objective markers.
 Patients should be motivated to engage in lifestyle modifications (see below).
Pharmacotherapy
Treatment of Crohn disease can be approached in two different ways: step-up therapy and top-down therapy.
MAXIMIZE TABLETABLE QUIZ
Overview of pharmacotherapy for Crohn disease [13][20]
Indication
Substance class
Symptomatic treatment
Acute
episode
Mild-tomoderate disease
Substances

Antidiarrheal agents


Loperamide
Bile acid binders

Topical corticosteroids

Triamcinolone

Topical 5-aminosalicylic acid derivatives (5-ASAs) (e.g., suppository, foam, enema)

Topical corticosteroids

Oral budesonide

Sulfonamides

Sulfasalazine

First-line: oral corticosteroids

Prednisone
Overview of pharmacotherapy for Crohn disease [13][20]
Indication
Substance class
Moderate-tosevere disease
Severe/fulminant
disease
Steroidrefractory disease
Azathioprine
6-Mercaptopurine
Alternatively
o Anti-p40 antibodies
o Alpha 4 integrin inhibitors


Ustekinumab (anti-p40 antibody)
Natalizumab, vedolizumab (alpha
4 integrin inhibitors)
First-line: IV corticosteroids

Methylprednisolone

Infliximab, adalimumab, certolizumab (TNFα antibodies)
If necessary: azathioprine (or 6mercaptopurine)
Steroid-sparing: thiopurine analogs





Maintenance therapy





Substances
First-line: TNF-α antibodies, if necessary
in combination with thiopurine analogs
Choice of substance depends on which agent
was used to induce remission
Corticosteroids are contraindicated for
maintenance.
5-ASA/sulfasalazine have proven to be
inefficient. [21]
The following substance classes are available:
o Thiopurine analogs
o Antimetabolites
o TNF-α antibodies
o Anti-p40 antibody
o Alpha 4 integrin inhibitors
Corticosteroids should not be used for long-term maintenance therapy!
Surgery
Overview






Azathioprine, 6-mercaptopurine (thiopurine
analogs)
Methotrexate (antimetabolite)
Infliximab, adalimumab, certolizumab (TNFα antibodies)
Ustekinumab (anti-p40 antibody)
Natalizumab, vedolizumab (alpha
4 integrin inhibitors)


Minimally-invasive resection of affected and nonfunctional intestinal loops while preserving as much intestinal length and function as possible
Indicated when medical therapy fails or patient develops severe complications (e.g., obstruction, stricture, abscess)
Methods
 Balloon dilatation: to treat intestinal stenosis
 Percutaneous drainage: prevents retention of secretions and abscessation
 Surgical drainage: when application of percutaneous drainage fails
 Strictureplasty
o A surgical procedure that opens up a bowel stricture without having to resect the bowel (bowel-sparing technique)
o Indicated after multiple resections
 Limited resection (e.g., proctocolectomy): in case of obstructions or strictures
Crohn disease is mainly treated with medication, but surgical interventions may be required to treat complications or if medical therapy fails.
Surgical intervention alone cannot cure Crohn disease and should therefore be considered as a last resort to avoid complications in which significant amounts
of bowel are lost (e.g., short bowel syndrome)!
Additional considerations
Lifestyle modifications
 Smoking cessation
 Avoiding certain drugs (e.g., NSAIDs
)
 Minimizing stress
Management of complications and comorbidities
 Malabsorption syndrome: appropriate substitution of vitamins, calories, protein, zinc, calcium, and iron
 Bile acid diarrhea: administration of ion-exchange resins to bind bile acids (e.g., cholestyramine)
 Depression and anxiety: See “Major depressive disorder” and “Generalized anxiety disorder.”
Prevention of malignancies
 Individuals with CD have an increased risk of cancer (especially of the small intestine, colon
, and lymphatics).
 Regular colonoscopies should be performed to minimize risk.
 People without major colonic involvement are managed according to the general screening guidelines (see ”Screening for colorectal cancer”)
 Nutrition
o Enteral nutrition always take preference over parenteral
o If oral food intake is not possible, nasogastric or nasoenteric tube should be used
o Secondary lactose intolerance (approx. 30% of cases): lactose-free diet [22]
o During acute episodes: avoid dietary fiber
NOTES
FEEDBACK
Complications
Intestinal complications
 Colorectal cancer (especially in the case of pancolitis)
 Short bowel syndrome and associated issues after surgery
 Stenosis/strictures → bowel obstruction/(sub)ileus
 Intestinal perforation → peritonitis
 Primary sclerosing cholangitis
 Impaired bile acid reabsorption
o Bile acid diarrhea
o Bile acid malabsorption → steatorrhea and deficiencies in fat-soluble vitamins
 Abscess formation/phlegmons: See below.
Intestinal fistulas and abscesses [23]
 Overview
o Typically involve the terminal ileum and/or perianal region
o Recurrences are common
o See “Anal abscess and fistula.”
 Etiology
o Iatrogenic (e.g., abdominal surgery, percutaneous drainage)
o Inflammation (e.g., inflammatory bowel disease, appendicitis)
 Pathophysiology [24]
o Inflammation → epithelial defects → epithelial-mesenchymal transition → deeper penetration of cell layers by epithelial cells → tissue damage
that organizes as tubular structures that ultimately connect to other organs or the surface
o After surgery or percutaneous drainage: deficient anastomoses/sutures or improper healing following intervention (e.g., due to reduced organ
blood flow) → leakage of intestinal contents → local infection → abscess formation and/or erosion → fistula formation
 Clinical features: depend on location of the fistula
o Enterovesical/colovesical fistula → pneumaturia (passing of urine together with air)/fecaluria (passing of stool together with urine)
→ recurrent urinary tract infections (UTIs)
o Enterocutaneous fistula → drainage of intestinal content through the skin
o Gastrocolic fistula → abdominal pain, weight loss, foul-smelling (feculent) belching
Systemic complications
 Signs of malabsorption syndrome
o Weight loss
o Failure to thrive and growth failure in children
o Anemia
 Iron deficiency anemia
Anemia of chronic disease
Megaloblastic anemia (vitamin B12 deficiency due to impaired absorption in the chronically inflamed ileum)
Osteoporosis


o
.

Amyloidosis
We list the most important complications. The selection is not exhaustive.
NOTES
FEEDBACK
Prognosis
 CD is a chronic disease that is currently not curable.
 Life expectancy is normal with proper treatment. [25]
 70–90% of all patients will require surgery at some point during their lifetime. [26]