Crohn’s disease and ulcerative colitis - How can they be differentiated?
Crohn’s disease and ulcerative colitis are both chronic inflammatory bowel diseases.
In this episode, we’ll discuss differences in the etiology, clinical features, and complications
of both conditions.
Etiology Let’s start with a quick comparison of the
etiologies.
Crohn’s disease and ulcerative colitis both have multifactorial etiologies, that is, a
number of causes have been suggested.
The most likely is a combination of genetic predisposition and environmental factors.
An important element in the pathophysiology of these diseases appears to be the impaired
mucosal barrier function of the bowel.
As a result, bacteria of the normal gut flora enter the mucosa and cause chronic inflammation.
In general, genetic predisposition is more pronounced in Crohn’s disease than in ulcerative
colitis.
This can be pinpointed by the following: Both diseases primarily occur between 15 and
35 years of age.
While Crohn’s disease may begin early in childhood, ulcerative colitis rarely occurs
in childhood and usually manifests after puberty.
A variety of genes are associated with both conditions.
One notable mutation can be found in the NOD2 gene, which is present in approximately half
of all patients with Crohn’s disease.
NOD2 mutations are more frequent in patients with childhood onset of disease.
In intestinal cells, NOD2 is important for identifying bacterial structures and activating
the immune system.
The NOD2 mutation can also be found in a small percentage of patients with ulcerative colitis,
but it remains unclear whether NOD2 plays a role in disease pathogenesis here.
Crohn’s disease is more common in smokers than in non-smokers.
Smokers are also affected with a more severe course of disease.
Therefore, patients with Crohn’s disease are urgently advised to stop smoking.
Interestingly, an opposing trend is observed in ulcerative colitis, in which smoking appears
to have a protective effect.
Smokers are less likely to develop ulcerative colitis than non-smokers.
The exact reason behind this correlation remains unknown, but it is likely due to the effect
of smoking on the T cell inflammatory response in the intestine.
Clinical findings Crohn’s disease can affect the entire gastrointestinal
tract, but is mainly localized in the terminal ileum.
In contrast, ulcerative colitis is, as the name indicates, limited to the rectum and
colon.
Crohn’s disease shows discontinuous involvement.
The occurrence of healthy areas of bowel interspersed with inflamed areas is termed skip lesions.
The word skip refers to the exclusion of some intestinal regions, while others are inflamed.
In ulcerative colitis, inflammation spreads continuously, usually beginning at the rectum
distally and extending proximally.
There are symptomatic differences between Crohn’s disease and ulcerative colitis.
Crohn’s disease frequently affects the small intestine and presents with watery, nonbloody
diarrhea.
The watery diarrhea occurs via two different mechanisms: Intestinal wall inflammation leads
to the secretion of water into the intestinal lumen.
In addition, there is malabsorption, which causes watery diarrhea due to osmotic processes.
In ulcerative colitis on the other hand, the diarrhea contains blood and mucus, and is
the result of exudative inflammation.
Bowel movements may be only slightly increased in Crohn’s disease.
In some cases, it may also be associated with constipation as a consequence of intestinal
stenosis.
Ulcerative colitis often demonstrates a marked increase in bowel movements.
Pain is usually localized to the right lower quadrant in Crohn’s disease and the left
lower quadrant in ulcerative colitis.
However, these localization patterns are only the most common, and do not represent a hard
and fast rule.
It is interesting to consider in ruling out potential differential diagnoses.
One example is acute appendicitis, which may be mistaken as an initial manifestation of
Crohn's disease.
In contrast, ulcerative colitis may sometimes mimic symptoms of diverticulitis.
However, since diverticular disease is relatively uncommon in patients under 40 years of age,
it is not as common a misdiagnosis as appendicitis is for Crohn’s disease.
Complications Crohn’s disease and ulcerative colitis are
associated with complications in the bowel and other organs.
These are referred to as intestinal and extraintestinal complications, respectively.
The intestinal complications of inflammatory bowel disease include stenoses, abscesses,
fistulas, and colorectal cancer.
Stenoses, abscesses, and fistulas are more common in Crohn’s disease.
Fistulas are present in up to 40% of cases and often the initial symptom in Crohn’s
disease.
This is caused by the spread of inflammation.
In Crohn’s disease, inflammation involves all intestinal layers, whereas in ulcerative
colitis, only the mucosa is affected.
Stenoses, abscesses, and fistulas are therefore more common in Crohn’s disease and are rare
in ulcerative colitis.
Colorectal cancer is more common in ulcerative colitis.
Malignant transformation is, in principle, possible in Crohn’s disease with colonic
involvement, but is considerably less frequent.
Extraintestinal complications Extraintestinal complications also occur in
both Crohn’s disease and ulcerative colitis.
Involvement of the small intestine plays a role in a number of extraintestinal complications.
Malabsorption syndrome with weight loss, vitamin B12 deficiency, and bile acid deficiency may
occur.
These substances may not be adequately absorbed as a result of inflammation of the small intestine,
particularly the terminal ileum.
These deficiency syndromes are more common in Crohn’s disease than in ulcerative colitis,
because Crohn’s disease frequently affects the small intestine.
They may also occur in ulcerative colitis, which is not always limited to the colorectum.
A so-called backwash ileitis can occur in ulcerative colitis.
The term backwash refers to a backward flow of intestinal contents from the cecum into
the ileum, which is believed to be the cause of inflammation.
However, the pathogenetic mechanism has not yet been fully elucidated.
There is also a group of extraintestinal manifestations based on autoimmune responses.
The exact mechanisms are not yet well understood.
Antibodies and T cells that are cross-reactive against other organs appear to be increasingly
formed in chronic inflammation.
There are a variety of extraintestinal manifestations.
Almost all organs can be affected, with the skin, eyes, joints, and liver most commonly
involved.
Extraintestinal manifestations occur more commonly in Crohn’s disease and primarily
involve the skin, eyes, and joints.
Liver involvement as a complication is more common in ulcerative colitis, in which primary
sclerosing cholangitis or, in short, PSC occurs.
Diagnostics How are Crohn’s disease and ulcerative colitis
diagnosed?
A suspected diagnosis is made based on the patient’s medical history and abdominal
ultrasound.
The final diagnosis is determined using three methods: endoscopy, imaging, and histology.
Endoscopy: The gold standard in diagnosis is endoscopy.
Typical characteristics in Crohn’s disease are a discontinuous pattern of involvement,
linear ulcers, also known as snail trails, a cobblestone appearance, and intestinal strictures.
In contrast, ulcerative colitis shows a continuous pattern of involvement, with other typical
characteristics including a reddened mucosa, bleeding on contact, and superficial ulcers.
Imaging: Imaging offers the possibility of examining
the small intestine, which cannot be fully achieved using colonoscopy or gastroduodenoscopy.
Radiography or MRI are typically used with an oral contrast agent.
Examination of the small intestine is also of particular interest, because Crohn’s
disease lesions, such as wall thickening or strictures, can be diagnosed.
In the image shown here, we can see a stricture in the terminal ileum.
Also, other complications such as fistulas and abscesses can be identified in MRI.
In addition to the small intestine, the colon can also be assessed.
In the advanced stages of ulcerative colitis, the colon has a pipe-like appearance.
This is due to the loss of haustral markings during the course of the disease, termed lead
pipe sign.
Histology: Using histological sampling, it is also possible
to differentiate between Crohn’s disease and ulcerative colitis.
Crohn’s disease is histologically characterised by non-caseating granulomas and giant cells.
They are found in approximately one-third of patients and are not present in ulcerative
colitis.
Possible histological findings in ulcerative colitis are crypt abscesses with granulocyte
infiltration.
Quiz Were you able to note all the differences
between ulcerative colitis and Crohn’s disease in terms of etiology, clinical features, complications,
and diagnostics?
In the following quiz, assign the statements to the corresponding inflammatory bowel disease.