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Crohn disease
This chronic condition causes inflammation that typically leads to symptoms like abdominal pain, severe diarrhoea, fatigue, and weight loss. It is a type of inflammatory bowel disease (IBD) and can affect individuals of any age.
Overview
Crohn disease is a chronic (long-term) condition characterised by inflammation of the digestive tract. It is one of the two main forms of inflammatory bowel disease (IBD), the other being ulcerative colitis. Unlike ulcerative colitis, which primarily affects the large intestine, Crohn disease can occur anywhere from the mouth to the anus, though it most commonly impacts the small intestine and the beginning of the large intestine [PMID:31548616]. The inflammation is often patchy, with healthy sections of bowel in between inflamed areas.
Symptoms & clinical features
The symptoms of Crohn disease can vary widely depending on which part of the digestive system is affected and the severity of the inflammation. Common symptoms include persistent abdominal pain, often accompanied by severe and frequent diarrhoea [PMID:24785420]. Other typical signs are unexplained weight loss, reduced appetite, and fatigue. Some individuals may experience anaemia due to blood loss or poor nutrient absorption. Less commonly, symptoms outside the digestive system, such as joint pain, skin rashes, or eye inflammation, can occur.
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Affected organs
While Crohn disease can affect any part of the gastrointestinal tract, the small intestine (particularly the ileum, its final section) and the colon (large intestine) are most frequently involved. Inflammation can penetrate deep into the layers of the bowel wall, leading to complications like strictures (narrowing of the intestine) or fistulas (abnormal connections between different parts of the bowel or between the bowel and other organs/skin). In severe cases, inflammation can lead to ulcers, abscesses, or blockages.
Risks & severity
The severity of Crohn disease varies significantly among individuals, ranging from mild to severe. It is a chronic condition, meaning symptoms can come and go, with periods of remission followed by flare-ups. Complications can include bowel strictures, fistulas, and abscesses, which may require surgical intervention. While Crohn disease can increase the risk of certain cancers, particularly colorectal cancer, regular surveillance and management can help mitigate this risk [PMID:24785420]. The condition typically emerges in adolescence or early adulthood, but it can be diagnosed at any age.
Genetic causes
Crohn disease is considered a complex or polygenic condition, meaning it is influenced by multiple genes acting together with environmental factors. Several genes have been identified that increase an individual's susceptibility to developing Crohn disease, including *NOD2*, *ATG16L1*, *IL23R*, and *IRGM* [PMID:25722425]. These genes play roles in crucial cellular processes such as the immune response, the body's ability to clear harmful bacteria (autophagy), and the signalling pathways involved in inflammation. Variants in these genes can disrupt these normal functions, contributing to the improper immune response seen in Crohn disease.
Inheritance pattern
Crohn disease does not follow a simple pattern of inheritance like some other genetic conditions. Instead, it is considered polygenic or complex, meaning that multiple genes contribute to an individual's risk, alongside environmental influences. While having a family member with Crohn disease can increase an individual's likelihood of developing the condition, it is not guaranteed. This means that a parent with Crohn disease does not necessarily pass the condition directly to their child, but rather a predisposition to it.
Diagnosis & testing
Diagnosing Crohn disease involves a combination of clinical assessment, blood tests, stool samples, endoscopic procedures (such as colonoscopy with biopsies), and imaging studies (like MRI or CT scans). Genetic testing is not typically used to diagnose Crohn disease directly, but research into genetic risk factors helps understanding of susceptibility. In the UK, if a doctor suspects Crohn disease, they would refer an individual for specialist assessment by a gastroenterologist. Diagnostic investigations would follow NHS pathways, and while there isn't a specific R-code for diagnostic genetic testing for Crohn disease itself, genetic counselling may be offered in some situations to discuss familial risk.
Management & lifestyle
While there is no cure for Crohn disease, various treatments aim to reduce inflammation, relieve symptoms, and prevent complications. Management typically involves medication, including anti-inflammatory drugs, immunosuppressants, and biological therapies. Dietary changes and nutritional support may also be recommended. In some cases, surgery may be necessary to remove damaged sections of the bowel or to treat complications like strictures or fistulas. Treatment plans are highly individualised and are managed by a gastroenterology team within the NHS, often involving specialist nurses and dietitians.
UK care pathway
In the UK, individuals suspected of having Crohn disease are typically referred by their GP to a gastroenterologist within the NHS. Diagnosis and ongoing management follow established NHS care pathways, often at specialist IBD clinics. Patients will have access to a multidisciplinary team, which may include gastroenterologists, specialist nurses, dietitians, and surgeons. If there are concerns about familial risk or complex hereditary patterns, referral to a clinical genetics service or a genetic counsellor can be arranged through the NHS Genomic Medicine Service (GMS) pathways, though specific R-codes for routine diagnostic sequencing for Crohn disease are not within the GMS national test directory.
Frequently asked questions
Is Crohn disease hereditary?
Crohn disease is not strictly hereditary in a simple way, but there is a genetic predisposition. This means that you have a higher chance of developing it if a close family member has the condition, but it's not guaranteed. Multiple genes, along with environmental factors, contribute to this risk.
What is the difference between Crohn disease and ulcerative colitis?
Both are types of inflammatory bowel disease (IBD). Ulcerative colitis only affects the large intestine (colon) and rectum, causing continuous inflammation in the innermost lining. Crohn disease can affect any part of the digestive tract, from mouth to anus, and the inflammation can be patchy and affect deeper layers of the bowel wall.
Can diet cure Crohn disease?
No, diet cannot cure Crohn disease, but it can play an important role in managing symptoms and reducing flare-ups for some individuals. A dietitian can help tailor a diet plan that considers your specific symptoms and nutritional needs. It's important to discuss any dietary changes with your healthcare team.
What are the common complications of Crohn disease?
Common complications include strictures (narrowing of the bowel), fistulas (tunnels between organs or to the skin), abscesses (pus-filled infections), and malnutrition due to poor nutrient absorption. In some cases, there can be an increased risk of colorectal cancer, which requires regular screening if affected portions are in the colon.
Will I need surgery for Crohn disease?
Not everyone with Crohn disease will need surgery. Medical treatments often successfully manage the condition. However, surgery may be necessary for complications like bowel blockages, severe strictures, fistulas, or if medication is not effective. Surgery is typically reserved for when other treatments have failed or for emergency situations.
References
- Crohn's disease. Nature reviews. Disease primers. 2020. PMID: 32242011
- Pogacnik JS, Salgado G. Perianal Crohn's Disease. Clinics in colon and rectal surgery. 2019. PMID: 31507348
- Leikin JB. Crohn's disease. Disease-a-month : DM. 2018. PMID: 28774635
- Kalla R, Ventham NT, Satsangi J. Crohn's disease. BMJ (Clinical research ed.). 2014. PMID: 25409896
- Dayan R, Sadownik L, Reutter J. Vulvar Crohn disease. CMAJ : Canadian Medical Association journal = journal de l'Association medicale canadienne. 2021. PMID: 33722830
- Long D. Crohn's Disease and Ulcerative Colitis: From Pathophysiology to Novel Therapeutic Approaches. Biomedicines. 2024. PMID: 38540302
- Rosevics L, Furlan TK, Waltrick CA. Tonsillar Crohn's Disease. United European gastroenterology journal. 2024. PMID: 39584787
- Hanauer SB. Targeting Crohn's disease. Lancet (London, England). 2017. PMID: 29096947