Title: IBS - pychological or bacterial?

Key words: prevalence, functional bowel disorders, psychological disorder, diagnostic criteria, gastro-enteritis, life-stress, hypochondria,

Date: June 2001

Category: Specific conditions

Type: Article

Author: Dr M Draper


IBS - pychological or bacterial?


Irritable bowel syndrome is a common condition affecting up to 20% of the Western population of adolescents and adults, with a higher prevalence in women (1).

Classified as one of the Functional Bowel disorders, the absence of distinct pathologiccal changes has inevitably led some physicians to consider it as a psychological disorder. Parallels with asthma should be drawn in that the symptoms can be arrived at via different mechanisms, including infection, allergy and psychological factors.

Although the diagnosis is made mainly on the history and exclusion of other pathologies (Helicobacter pylori, inflammatory bowel disease, parasites, tumours etc.) the condition has clear diagnostic criteria (2,3) including: Continuous or recurrent symptoms for at least 3 months of:

1. Abdominal pain relieved by defaecation or associated with a change in frequency or consistency of stool.

2. disturbed defaecation at least 25% of the time: 3 or more of:

# altered stool frequency

# altered stool form (hard or loose/watery)

# altered stool passage (straining, urgency or tenesmus)

# passage of mucous

# abdominal distension These diagnostic criteria do not fully paint the extremely variable nature of the condition, associated features such as offensive wind and worsening during times of stress. Rectal bleeding was reported by 35% of IBS cases and in one study only half of them had haemorrhoids (4).


Evidence for IBS being a bacterial problem:

In a sample of 94 patients with acute gastro-enteritis studied at an infectious unit, 22 (23%) were found three months later to fulfil the Rome criteria for IBS (5). When comparing this group of symptomatic patients (IBS+) to the remaining sample (IBS-), three major findings were noted:

(a) Psychosocial difficulties were again shown to influence which patients with acute gastro-enteritis would remain symptomatic. Pre-existent life stress and hypochondriasis were the strongest predictors for the IBS+ group, and the development of IBS-like symptoms was not explained by illness behaviour.

(b) Acute gastroenteritis was associated with increased numbers of rectal inflammatory cells relative to biopsy samples from a healthy group.

(c) When compared with healthy controls, those with acute gastroenteritis went on at three months to develop physiological evidence of gut dysfunction - reduced whole gut transit time, decreased sensation threshold to rectal distension, decreased rectal compliance and reduced number of rectal contractions. The possible mechanisms involved are discussed in detail by Drossman (6). Psychometric scores and persistence of irritable bowel symptoms 6 months after infectious diarrhoea again drew the conclusion that psychological factors are important in IBS (7). a longer term study (one year) of adults between 25-74 years old who had had bacterial gastroenteritis showed a 12 fold increase in IBS compared to the normal population (8).

Instability in the faecal flora with higher counts of facultative bacteria (9) or higher proportions of gram-negative facultative bacteria (10) and abnormal fermentation, particularily of hydrogen, is greater in patients with IBS than controls, and both symptoms and gas production are reduced by an exclusion diet (11). Antibiotics (12) and dietary fibre (13), by disturbing the colonic bacteria, may contribute to the development of IBS and food intolerances. In one self-reporting questionnaire study (14) the odds of having IBS was higher among subjects who regularily used analgesics (Acetaminophen, aspirin or NSAI's) for non-IBS symptoms and had higher intolerances to food.



Good evidence exists that bacterial dysbiosis and psychological factors contribute to the development and continuance of IBS. The holistic approach to the patient with IBS offers the best strategy so that all components of the condition can receive the appropriate support and treatment.



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