Misdiagnosis of Irritable Bowel Syndrome

The emergence of any ‘red flag’ symptoms during management and follow-up should prompt further investigation and/or referral to secondary care.

• Emphasise the importance of self-help
• Encourage relaxation time and increasing levels of physical activity
• Have regular meals and take time to eat
• Drink 8 cups of fluid and limit caffeinated drinks to 3 cups a day
• Reduce fizzy drink intake and alcohol
• Avoid sorbitol
• Reduce fibre intake although people with bloating and wind may benefit from soluble fibre (ispaghula / oats/linseeds)
• Consider referral to a dietitian
• Consider anti-spasmodics
• Laxatives for constipation symptoms (avoid lactulose), loperamide for diarrhoeal symtoms
• Low-dose tri-cyclic antidepressants if anti-spasmodics, laxatives and anti-diarrhoeals have not worked.
• Consider SSRIs or psychological therapies (CBT, hypnotherapy) who do not respond to the above after 12 months.

The prevalence of IBS is approximately 10% based on a community survey in England (2). Higher rates have been reported (3) and females are affected more frequently than males. The symptoms referred to in the NICE guidelines are broadly the same as those defined for IBS in the ROME III CRITERIA for functional gastointestinal disorders.

There is no consistent biological marker for IBS and therefore symptoms have to be used to make a clinical diagnosis, as dictated by the NICE guidelines or Rome criteria. However, symptoms are difficult to quantify objectively and can vary amongst individuals with IBS (3). The symptoms of many organic conditions can overlap with those of IBS which unsettles both patients and doctors. For this reason, many doctors treat IBS as a diagnosis of exclusion. Evidence for this stems from community-based surveys showing that up to 50% patients with IBS undergo colonoscopy as part of their diagnostic work-up(4).

16% patients with IBS are referred to secondary care and 26% have multiple GP attendances (2). A survey of doctors’ attitudes to IBS has shown that only a fraction of doctors are content at making a diagnosis of IBS without further investigations (5).

Conversely, the strict Rome criteria for IBS, originally developed for clinical trial purposes, has proven to be reliable in terms of positive predictive value. In a prospective study, the application of the Rome criteria and absence of red-flags carried a 98% positive predictive value in the diagnosis of IBS (one patient’s diagnosis was revised to proctitis and another’s was revised to hyperthyroidism) (6). In simple terms, only 2% of patients who fit the IBS criteria were demonstrated to have a different diagnosis after 2 years of follow-up. A systematic review of the use of diagnostic tests in patients who fit diagnostic criteria for IBS has shown that the risk of organic gastointestinal disease in these patients is less than 1% (7). This study also demonstrated that the probability of coeliacs disease in IBS patients is ten times higher than the general population, hence the NICE recommendations for antibody screening.

Despite this low risk of organic disease in patients fulfilling IBS diagnostic criteria, the high prevalence of IBS in the population equates to a potential large number of misdiagnoses. A large cohort study of nearly 60 000 IBS patients revealed no increased risk of colorectal cancer in the period starting one year after the diagnosis of IBS. However, in the first 3 months following the diagnosis of IBS, there was an 8-fold increased risk of colon cancer and 5-fold increased risk of rectal cancer (8).

If both IBS and colorectal cancer had common risk factors, or IBS was a risk factor for colorectal cancer, one would expect to see increases in incidence with time. This study therefore strongly argues that some patients with colorectal cancer are misdiagnosed with IBS. Similar findings were observed in a smaller UK study (9). Whether red flag symptoms developed following the diagnosis of IBS, prompting further investigation is not known.

Doctors diagnosing IBS might therefore be concerned about the possibility of legal repurcussions if organic disease is later apparent. However, testing according to NICE guidelines is safe and protects against legal claims for complications arising from “unnecessary” testing (10).