IBS Fact : Evidence-based management of irritable bowel syndrome

Coeliac disease vs irritable bowel syndrome (IBS)

Coeliac disease is a chronic inflammation of the small intestine caused by an immune reaction to dietary gluten, a protein contained in wheat, barley, and rye. Upon ingestion, gluten provokes an immune response that attacks the body’s own intestinal tissue. Hence, coeliac disease is not an allergy but an autoimmune disease. Coeliac disease has a strong genetic component, affecting almost exclusively those with genetic susceptibility. The inflammatory response results in damage of the intestinal lining causing abdominal complaints and malabsorption of nutrients. Coeliac disease occurs in about 1% of the population worldwide. Symptoms can include diarrhoea, fatty stools, weight loss, bloating, flatulence and abdominal pain. Extra-intestinal symptoms such as anaemia, osteoporosis, and skin disorders are also common. However, many individuals with coeliac disease may have no symptoms at all. Diagnosis of coeliac disease consists of several steps and should be performed by a gastroenterologist. The first step consists of serologic (blood) testing for elevated autoantibodies while on a gluten-containing diet. Here, the two most effective tests are the IgA anti-transglutaminase antibody test (TTG) and the IgA anti-endomysial antibody test (EMA). Positive results for one of these antibodies indicate a high likelihood of CD, with each test having greater than 90% sensitivity. However, approximately 3% of patients with coeliac disease have a deficiency in total IgA. Thus, despite suffering from coeliac disease, they may present falsely negative blood test results. In such patients, measuring total IgA levels may be performed in addition to the above blood tests. In patients testing positive for either TTG or EMA, the next step in the diagnosis consists of an endoscopic collection of tissue samples (biopsy) from the small bowel to assess tissue damage, again while on a gluten-containing diet. Together, the positive blood tests and intestinal tissue damage confirmed by biopsy indicate coeliac disease with 99% specificity. The diagnosis of coeliac disease is then definitively confirmed by an improvement of symptoms and a decrease of specific antibodies after introducing a gluten-free diet. Guidelines for diagnosing coeliac disease are continuously being updated, and with the improving accuracy of blood tests and the development of new disease markers, invasive endoscopic biopsies can be expected to become less important. As mentioned above, genetic predisposition plays an important role in coeliac disease. In fact, coeliac disease does not develop unless a person carries either the so called HLA-DQ2 or HLA-DQ8 gene variant, also known as an allele. However, these gene variants are also very common among the general population (30 – 40%) and do not cause coeliac disease in most persons. Thus, although HLA-DQ2 or HLA-DQ8 is necessary for the development of the disease, it is not sufficient. Testing for the presence of HLA-DQ2 or DQ8 may be, however, useful in persons with a family history of coeliac disease or those in whom diagnosis is uncertain. Here, negative results for both genes practically exclude the diagnosis of coeliac disease (<1% likelihood of the disease being present), while positive results only indicate a relative risk of 36 -53% and will still require further workup. The above screening methods will also identify patients with wheat allergy or a, so called, non-celiac gluten sensitivity. In such patients, symptoms improve considerably when on a gluten free diet despite negative blood test and genetic screening for coeliac disease. Currently, no curative treatment exists for coeliac disease, and the only option available is a strict life-long gluten free diet. Such diets require significant education, motivation, and follow-up and should be initiated only after a definitive diagnosis has been made. This is particularly important since avoidance of gluten during coeliac disease screening may cause false negative results. Because of similar symptoms, coeliac disease may be mistakenly diagnosed as IBS. Indeed, studies have shown a 4.5% prevalence of coeliac disease in patients clinically diagnosed with IBS. Other studies have concluded that coeliac disease, as diagnosed by serologic testing and biopsy, is four times more prevalent among patients with a clinical presentation of IBS than in non-IBS populations. Because of this overlap, patients with IBS symptoms should consider coeliac screening. This applies in particular to those with diarrhoea and anaemia and to first-degree relatives of confirmed coeliac disease sufferers.

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