Inflammatory Bowel Disease
Inflammatory bowel disease (IBD) is a group of chronic inflammatory conditions of the gastrointestinal tract that most commonly includes Crohn’s disease and ulcerative colitis. Both conditions cause inflammation of the digestive tract but differ in the specific patterns of involvement, features, and management. Crohn’s disease can affect any part of the gastrointestinal tract (most commonly the small bowel and colon) and typically involves the full thickness of the bowel wall in a patchy distribution. Ulcerative colitis affects the inner lining of the colon and rectum in a continuous distribution. Symptoms typically include abdominal pain, diarrhea (often with blood in ulcerative colitis), weight loss, and fatigue, and can range from mild to severe. Treatment has advanced substantially with the availability of newer medications, and care is coordinated by gastroenterologists and other specialists.
What is it?
Inflammatory bowel disease (IBD) refers to a group of chronic inflammatory conditions of the gastrointestinal tract. The two most common forms are Crohn’s disease and ulcerative colitis, which share some features but differ in important ways. A small proportion of IBD cases have features overlapping both conditions and are called indeterminate or unclassified IBD.
The exact cause of IBD is not fully understood but appears to involve an abnormal immune response to intestinal bacteria in genetically susceptible individuals, influenced by various environmental factors. Multiple genes have been associated with increased risk, and family history is a significant risk factor. Environmental factors include smoking (which paradoxically increases the risk of Crohn’s disease but may reduce the risk of ulcerative colitis), diet (with emerging evidence about specific dietary factors), certain medications (such as NSAIDs, which can precipitate flares), infections, geography (with higher rates in developed countries), and the intestinal microbiome. IBD is neither contagious nor caused by specific dietary choices, though diet can affect symptoms.
Crohn’s disease can affect any part of the gastrointestinal tract from the mouth to the anus but most commonly involves the terminal ileum (the last part of the small bowel) and the colon. Its characteristic features include patchy involvement with normal areas (“skip lesions”) between affected areas, inflammation that extends through the full thickness of the bowel wall (transmural inflammation, in contrast to ulcerative colitis which is limited to the inner lining), and formation of complications such as strictures (narrowings), fistulas (abnormal connections between the bowel and other structures), and abscesses. Perianal disease (fistulas, abscesses, and skin tags around the anus) is a common and often challenging feature of Crohn’s disease. The transmural inflammation and complication-prone nature of Crohn’s disease distinguish it from ulcerative colitis.
Ulcerative colitis affects only the colon and rectum, involves only the inner lining of the bowel (not the deeper layers), and typically has continuous inflammation starting from the rectum and extending upward for a variable distance (from involvement of only the rectum, called proctitis; to involvement of the left side of the colon; to involvement of the entire colon, called pancolitis). Because inflammation is limited to the inner lining, complications such as fistulas and abscesses are much less common than in Crohn’s disease, though ulcerative colitis has its own set of complications including severe flares that can be life-threatening.
Both conditions are chronic and typically follow a course of flares (periods of active symptoms and inflammation) alternating with periods of remission (few or no symptoms). The severity, frequency, and pattern of flares vary significantly among patients. Effective treatment can significantly reduce the frequency and severity of flares and maintain remission.
Symptoms of IBD depend on the specific type, location of involvement, and severity. Common symptoms include:
Chronic diarrhea, often more than 3 loose or watery stools per day, sometimes with mucus. In ulcerative colitis, blood is typically visible in the stool, while in Crohn’s disease, visible blood may or may not be present depending on the location and severity.
Abdominal pain, which varies with the location of involvement. In Crohn’s disease, pain is often in the lower right abdomen (with terminal ileal involvement) or more diffuse. In ulcerative colitis, pain may be cramping and often occurs before bowel movements.
Unintended weight loss and reduced appetite.
Fatigue, often significant.
Fever, particularly during flares or with complications such as abscesses.
Urgency to have bowel movements and, in ulcerative colitis, a sensation of incomplete emptying (tenesmus).
Complications specific to Crohn’s disease may include symptoms of stricture (colicky abdominal pain, nausea, vomiting, symptoms of bowel obstruction), fistulas (abnormal connections producing symptoms such as passing air or stool through the vagina or from the skin, urinary tract infections from a bowel-to-bladder fistula, or drainage from the skin), abscesses (localized areas of infection presenting with pain, fever, and tenderness), and perianal disease (fistulas, abscesses, or skin tags around the anus).
Extraintestinal manifestations—symptoms outside the bowel that are related to the underlying immune process—can occur in both Crohn’s disease and ulcerative colitis. These may include:
– Joint pain and inflammation (arthritis, particularly affecting the sacroiliac joints and, less commonly, other joints)
– Skin conditions (erythema nodosum, which causes tender red bumps typically on the shins; pyoderma gangrenosum, a rarer more severe skin condition)
– Eye inflammation (uveitis, episcleritis)
– Liver conditions (primary sclerosing cholangitis, a chronic bile duct condition more common in ulcerative colitis)
– Kidney stones
– Osteoporosis (bone thinning)
– Blood clots (increased risk during flares)
In children and adolescents, IBD can also cause growth delay and delayed puberty.
Diagnosis of IBD typically involves several components.
Colonoscopy with biopsy is the primary diagnostic tool. It allows direct visualization of the colon and terminal ileum, identification of characteristic patterns of inflammation, and biopsy for confirmation. Endoscopic features can help distinguish Crohn’s disease (patchy involvement, skip lesions, deep ulcers, cobblestoning appearance, terminal ileal involvement) from ulcerative colitis (continuous involvement starting from the rectum, more uniform inflammation limited to the inner lining).
Upper endoscopy may be performed, particularly when Crohn’s disease is suspected, to evaluate for involvement of the esophagus, stomach, or duodenum.
Imaging is important for evaluating small bowel involvement (which cannot be reached with standard endoscopy) and complications. CT enterography and MR enterography are dedicated protocols for small bowel evaluation. MR enterography avoids radiation and is often preferred for young patients and for repeated imaging over time. These studies show the thickness and enhancement of the bowel wall, the length of involved segments, complications such as strictures, fistulas, and abscesses, and the appearance of the mesentery.
Standard CT of the abdomen and pelvis is useful for evaluation of complications such as abscess or perforation.
Capsule endoscopy may be used to evaluate for subtle small bowel involvement in Crohn’s disease when other studies are inconclusive, though it is generally avoided when strictures are suspected (because of the risk of capsule retention).
Blood tests typically include complete blood count (which may show anemia and elevated white blood cell count), inflammatory markers (C-reactive protein, or CRP, and erythrocyte sedimentation rate, or ESR), kidney and liver function, and, when appropriate, tests for specific antibodies (such as ASCA, associated with Crohn’s disease, and p-ANCA, associated with ulcerative colitis, though these are supportive rather than definitively diagnostic), nutritional status (iron, vitamin B12, vitamin D), and screening for infections that could complicate treatment.
Stool tests are important, particularly at initial evaluation and during flares. Fecal calprotectin is a marker of intestinal inflammation and can help distinguish IBD from non-inflammatory conditions such as irritable bowel syndrome, and monitor disease activity over time. Stool cultures and testing for Clostridioides difficile are important to exclude infection, which can mimic or complicate IBD.
Distinguishing Crohn’s disease from ulcerative colitis, and both from other conditions, is important because the management differs. In some cases, the distinction is not immediately clear, and the diagnosis may become more apparent over time.
Important to Know
Management of inflammatory bowel disease has advanced substantially over the past two decades with the availability of newer medications and treatment strategies. Care is best coordinated by gastroenterologists (particularly those with IBD expertise), and often involves multidisciplinary teams including colorectal surgeons, nutritionists, and, when needed, other specialists including rheumatologists, dermatologists, ophthalmologists, and mental health professionals.
Modern IBD management increasingly focuses on early effective treatment to prevent complications rather than waiting for complications to develop. The goals of treatment include controlling active inflammation (inducing remission), maintaining remission over the long term, healing the bowel lining (mucosal healing), preventing complications, and preserving quality of life.
Medications for IBD include several classes:
Aminosalicylates (5-aminosalicylic acid, or 5-ASA compounds, including mesalamine and others) are anti-inflammatory medications used primarily for mild-to-moderate ulcerative colitis, where they are often first-line treatment. They have limited efficacy in Crohn’s disease and are used less commonly in that condition.
Corticosteroids (such as prednisone, methylprednisolone, and, for lower GI-limited effect, budesonide) are effective for treating flares but are not appropriate for long-term maintenance due to significant side effects. They are typically used for induction of remission and then tapered.
Immunomodulators (such as azathioprine, 6-mercaptopurine, and methotrexate) are used to maintain remission and to reduce corticosteroid needs. They act more slowly than corticosteroids and are generally started with the expectation of long-term use.
Biologic therapies have transformed IBD treatment and include several classes:
– Anti-TNF (tumor necrosis factor) agents (such as infliximab, adalimumab, certolizumab pegol, and golimumab) target inflammatory signaling; they are effective for both Crohn’s disease and ulcerative colitis
– Anti-integrin agents (such as vedolizumab) specifically target immune cell trafficking to the gut
– Anti-IL-12/23 agents (such as ustekinumab) target other inflammatory pathways
– Anti-IL-23 agents (such as risankizumab, mirikizumab, and guselkumab) more specifically target the IL-23 pathway
– Others in this rapidly evolving category
Small molecule targeted therapies:
– JAK inhibitors (such as tofacitinib, upadacitinib) block intracellular inflammatory signaling
– Sphingosine-1-phosphate (S1P) receptor modulators (such as ozanimod, etrasimod) affect immune cell trafficking
Treatment selection depends on the specific type of IBD, severity, location of involvement, response to prior treatments, patient factors (including preferences, comorbidities, insurance coverage, and, in appropriate patients, planning for pregnancy), and specific characteristics of the disease. Modern approaches often involve early treatment with more effective agents in patients with high-risk features rather than a step-wise approach that historically began with milder medications, based on evidence that early effective treatment improves long-term outcomes.
Regular monitoring during treatment includes clinical assessment, blood tests, stool tests (particularly fecal calprotectin), imaging (particularly MR enterography in Crohn’s disease), and periodic endoscopy to assess mucosal healing.
Surgery has an important role in both conditions.
For Crohn’s disease, surgery is often needed for complications such as strictures (which may require dilation or surgical resection), fistulas (which may require various surgical approaches), abscesses (which may require drainage), and perianal disease. Surgery does not cure Crohn’s disease—the disease can recur after surgery—but can effectively address complications. A common surgical procedure is ileocecal resection for terminal ileal disease.
For ulcerative colitis, surgery (typically total proctocolectomy with construction of a J-pouch, or in some cases with permanent ileostomy) can be curative because the disease is limited to the colon and rectum. Surgery is considered for patients with severe or refractory disease, complications such as toxic megacolon, dysplasia or cancer, or patient preference. The most common current approach is restorative proctocolectomy with ileal pouch-anal anastomosis (IPAA, or “J-pouch”), which allows bowel movements through the natural anal route without a permanent stoma. Some patients require or prefer permanent ileostomy.
Nutritional support is important for many patients with IBD, particularly those with weight loss, malabsorption, small bowel involvement, or specific deficiencies. Consultation with dietitians experienced in IBD is valuable. Specific dietary approaches (such as exclusive enteral nutrition, particularly in pediatric Crohn’s disease) can be highly effective for some patients.
Management of extraintestinal manifestations is often coordinated with the treatment of the underlying IBD, as many extraintestinal symptoms improve with control of the underlying disease. Some manifestations (such as primary sclerosing cholangitis) follow their own course and require specific management.
Cancer surveillance is important, particularly for patients with long-standing colonic IBD. Regular colonoscopy with careful examination and biopsies is recommended, with the specific frequency and approach determined by disease duration, extent, and other risk factors. Patients with primary sclerosing cholangitis have particularly elevated cancer risk.
Care during pregnancy in patients with IBD requires special attention, and coordination with gastroenterology, obstetrics, and, when appropriate, maternal-fetal medicine is important. Most IBD medications are compatible with pregnancy, and active disease during pregnancy generally poses more risk than well-controlled disease. Family planning is best discussed before pregnancy when possible.
For patients considering fertility preservation before treatment, coordination with reproductive medicine is important.
Vaccinations are particularly important for patients with IBD, especially those on immunosuppressive therapy. Live vaccines have specific considerations. Coordination with primary care is important.
Mental health considerations are important, as IBD can significantly affect quality of life, and depression and anxiety are more common in IBD patients. Mental health support is a valuable component of comprehensive care.
Support groups and organizations focused on IBD (such as the Crohn’s & Colitis Foundation) provide valuable information, community, and resources.
Care is typically coordinated by gastroenterologists with IBD expertise, and often involves multidisciplinary teams. Imaging, laboratory, endoscopic, and clinical findings are interpreted alongside the patient’s symptoms, examination, and broader clinical context rather than in isolation.
Patient education plays an essential role. Understanding the diagnosis, the specific type of IBD, the rationale for the treatment plan, the importance of medication adherence, the meaning of monitoring tests, warning signs of flares or complications, the importance of vaccinations, and, when relevant, the specific considerations for pregnancy or surgery all contribute to better outcomes.
Red flag symptoms include severe abdominal pain, symptoms of bowel obstruction (severe abdominal pain, distention, vomiting, inability to pass stool or gas), significant gastrointestinal bleeding (large amounts of visible blood, black tarry stools, or lightheadedness with bleeding), high fever with signs of severe infection or sepsis (particularly in patients on immunosuppressive therapy), sudden severe abdominal pain (which may suggest perforation or toxic megacolon), signs of severe dehydration, severe joint pain with fever, sudden severe headache with fever (which may suggest infection in immunosuppressed patients), sudden vision changes with severe eye pain, and rapid clinical deterioration. These warrant prompt or urgent medical evaluation.