Intestinal Disease: Types, Symptoms and Diagnosis

How the intestines work

The small intestine is about 6 m (20 ft) long. It has three parts: the duodenum, jejunum and ileum. It digests food and absorbs nutrients, so diseases here often cause weight loss, deficiencies and watery diarrhea. The large intestine (colon, about 1.5 m or 5 ft, ending in the rectum) absorbs water and stores stool, so diseases here often cause changes in stool, bleeding and urgency.

Main types of intestinal disease

Symptoms

• abdominal pain or cramps
• bloating and gas
• diarrhea, constipation or alternating between the two
• urgency, or a feeling of incomplete emptying
• mucus or blood in the stool
• nausea and vomiting
• weight loss, tiredness and anemia from poor absorption or blood loss
• symptoms outside the gut in IBD and celiac disease: joint pain, mouth ulcers, skin rashes, eye inflammation

Signs that point away from IBS

IBS does not cause bleeding, weight loss, fever, anemia or symptoms that wake you at night. If any of these are present, doctors look for an inflammatory, infectious or structural cause.

Causes and risk factors

• Genes and family history: IBD, celiac disease and colorectal cancer run in families.
• Infections: contaminated food or water, recent antibiotics (for C. difficile), travel.
• Diet: low fiber raises the risk of constipation and diverticular disease; red and processed meat raise colorectal cancer risk.
• Smoking: increases the risk and severity of Crohn's disease.
• Medicines: NSAIDs can cause ulcers and bleeding in the small bowel; opioids cause constipation.
• Age: diverticular disease, ischemia and cancer become more common after 50.
• Previous surgery: adhesions can cause obstruction years later.

How intestinal disease is diagnosed

1. History and exam: pattern of symptoms, diet, travel, medicines, family history.
2. Blood tests: blood count (anemia), inflammation markers (CRP), celiac antibodies (tTG-IgA), iron, B12, folate and liver tests.
3. Stool tests: infection screens, fecal calprotectin (a marker that separates inflammation from IBS) and fecal immunochemical testing (FIT) for hidden blood.
4. Colonoscopy: a camera through the rectum to view the colon and end of the small bowel, take biopsies and remove polyps.
5. Upper endoscopy: to biopsy the duodenum for celiac disease.
6. Imaging: CT for diverticulitis and obstruction; MR enterography or capsule endoscopy for the small bowel.
7. Breath tests: for lactose intolerance and SIBO.

Treatment

Treatment depends on the specific disease:

• IBS: diet changes such as the low-FODMAP diet under guidance, fiber, antispasmodics, gut-directed therapy and medicines targeting diarrhea or constipation.
• Celiac disease: a strict lifelong gluten-free diet.
• IBD: aminosalicylates, steroids for flares, immune-modifying drugs and biologics; surgery for complications.
• Infections: fluids and rest; antibiotics or antiparasitics for specific infections.
• Diverticulitis: often managed at home with rest and diet, with antibiotics for complicated cases; surgery for recurrent or severe disease.
• Obstruction: bowel rest, a tube to decompress the stomach, and sometimes surgery.
• Cancer: surgery, chemotherapy, radiotherapy and targeted therapy.

Prevention and screening

• Eat 25 to 35 g of fiber a day from vegetables, fruit, legumes and whole grains, and drink enough fluids.
• Do not smoke, and limit alcohol and processed meat.
• Wash hands and practice food safety to avoid infections.
• Use NSAIDs sparingly.
• Start colorectal cancer screening at age 45 if you are at average risk, or earlier if you have a family history.

Frequently asked questions

What are the most common intestinal diseases?

The most common are irritable bowel syndrome, viral gastroenteritis, chronic constipation, diverticular disease, lactose intolerance and hemorrhoids. Celiac disease, Crohn's disease and ulcerative colitis are less common but important. Colorectal cancer is one of the most common cancers in adults.

What are the warning signs of a serious bowel disease?

Blood in the stool, black stools, unexplained weight loss, anemia, persistent diarrhea, symptoms that wake you at night, fever, and a lasting change in bowel habit after age 45 all need medical evaluation. A family history of bowel cancer or IBD lowers the threshold for testing.

How do doctors tell IBS from inflammatory bowel disease?

IBS causes pain and bowel changes but no inflammation, bleeding or weight loss, and tests are normal. IBD causes visible inflammation. A fecal calprotectin stool test is often the first step: a normal result makes IBD unlikely, while a high result leads to colonoscopy.

Can intestinal disease be cured?

Some can. Infections usually clear completely, and early colorectal cancer can be cured with surgery. Celiac disease is controlled by a gluten-free diet. IBS, Crohn's disease and ulcerative colitis are long-term conditions, but most people achieve good control with treatment.