Inflammatory bowel disease

Inflammatory bowel disease (IBD) is an umbrella term for two idiopathic conditions; Crohn disease (CD) and ulcerative colitis (UC). Both are chronic diseases of the gastrointestinal tract that involve some inappropriate immune activation of the mucosa. Luckily for medical students the two diseases have different features that can be used to differentiate them.

IBD is a chronic disease, but it isn’t always active. There are usually periods of active disease with weeks or months of asymptomatic periods between them. The asymptomatic periods are called remission while the symptomatic periods are called flares. Several factors may provoke a flare-up, like stress, specific types of food, or cigarette smoking. However, most flares occur without an apparent trigger.

Crohn disease

Crohn disease may affect the entire GI tract, from the rectum to the oral cavity. It most frequently affects the terminal ileum and coecum.

Diagnosis and evaluation

Diagnosis of CD is histological, requiring biopsy. The workup of CD involves MR enterography (to visualise the small bowels) and colonoscopy. Biopsies should be taken from any lesions visible, as well as the terminal ileum. If there are oesophageal or gastric symptoms, upper endoscopy should be performed as well. Laboratory tests should check for anaemia and vitamin deficiencies.

Non-infectious intestinal inflammation correlates directly with the amount of calprotectin in the faeces. Measurement of this protein is useful both for excluding the diagnosis (if negative) and for follow-up (to detect flares). CRP and ESR may be elevated in severe cases. Anti-saccharomyces cerevisiae antibodies (ASCA) is specific for Crohn disease and can be used to distinguish it from UC in uncertain cases.

Ulcerative colitis

UC is similar to Crohn disease in some ways but different in many other. The biggest difference perhaps is that UC can only affect the colon, and that the inflammation is never deeper than the submucosa. Because ulcerative colitis only affects the colon, it can be cured by total colectomy.

Diagnosis and evaluation

Colonoscopy with biopsy is essential. The diagnosis of UC is made in the patient with chronic diarrhoea, colitis on biopsy, and when other causes of diarrhoea have been ruled out.

Stool should be tested for bacterial causes of diarrhoea. P-ANCA is positive in UC and negative in CD and so can be used to distinguish the two. Faecal calprotectin is elevated in UC as well.

Colorectal cancer

Colorectal carcinoma (CRC) refers to all cancers that can affect the colon and rectum. Carcinomas in the colon are the most common malignancy in the GI-tract, accounting for 95% of all GI cancers. CEA is the tumour marker most specific for CRC and should be measured upon diagnosis. Elevated CEA is associated with a worse prognosis, and CEA which doesn’t normalise postoperatively is indicative of persistent disease. Microcytic or normocytic anaemia (due to chronic GI blood loss) or faecal occult blood are typical findings in CRC.

Malabsorption

Malabsorption syndrome refers to a number of disorders in which the small intestine can’t properly absorb one or more nutrients. This may be due to impaired absorption or impaired digestion.

Diagnosis and evaluation

Many tests can be useful in the evaluation of malabsorption:

Serum ferritin – marker of iron absorption
Serum protein and albumin– marker of protein absorption
Microscopic examination of fat content in stool – marker of fat absorption
Hydrogen breath test – test for carbohydrate absorption
- After consumption of a carbohydrate (usually lactose), serial measurements of hydrogen in the breath are made. Abnormally high levels of hydrogen in the breath in a sign of malabsorption of that carbohydrate
D-xylose absorption test – test for small bowel mucosal defects
- D-xylose is passively absorbed through healthy bowel mucosa. If, following administration of this monosaccharide, serum and urine levels are low, it can be concluded that the bowel mucosa has defects
Stool culture – for parasites which impair absorption
Bile salt breath test/SeHCAT test – test for bile salt absorption, no longer used
Shilling test – test for B12 absorption, no longer used