IBS is considered as a functional gastrointestinal disorder, so-called because it was believed that most of the symptoms originated in the central nervous system.
IBS is the most common diagnosis in gastroenterology clinics reaching up to 50% of consultations. Over 40% of patients with IBS exhibit avoidance of normal social activities ranging from exclusion of food types to avoidance of work and leisure related activities.
Physical symptom severity, psychological and social dysfunction in a series of outpatients with irritable bowel syndrome, 1990
DEFINITION
IBS is defined as a functional bowel disorder in which chronic abdominal pain is associated with defecation or a change in bowel habit, with features of disordered defecation and distension and visceral hypersensitivity.
We distinguishes three different subtypes based on the predominant symptoms: IBS-A (pain-predominant), IBS-C (constipation-predominant) and IBS-D (diarrhoea-predominant).
EPIDEMIOLOGY
This condition is ubiquitous and has been found in every country in which it has been sought.
IBS patients, in common with other sufferers from functional GI disorders, are more anxious than healthy controls, showing greater anxiety and depression. They also show a greater lifetime incidence of treatment for anxiety and depression. Anxiety should not influence one’s workup of a patient, since it does not help significantly in making the diagnosis; however, it should and does influence management once the diagnosis has been established.
Some sex differences in terms of symptom expression in irritable bowel syndrome have been recorded, with more women than men reporting the disorder, although symptom severity, illness effect, and psychological distress levels seem to be similar in men and women. Constipation, distension, mucus, and nausea are more frequent in women than men.
Gender differences in irritable bowel symptoms, 1997
SYMPTOMS
The most common symptoms are diarrhoea, constipation, abdominal pain and bloating.
The main features are recurrent abdominal pain and/or discomfort, whose clear relationship to changes in stool frequency or consistency and its relief by defecation implies that they originate in the colon. This relationship distinguishes abdominal pain due to colonic dysfunction from that due to gynaecological, urinary or musculoskeletal disorders.
In addition to these gastrointestinal (GI) symptoms, patients commonly report non-GI symptoms of lassitude, headache, backache, dysmenorrhoea, and dyspareunia.
Symptoms characteristically wax and wane and patients typically have pain a median of 3 days a week.
DIAGNOSIS
There is presently no established biological marker for irritable bowel syndrome.
The diagnosis of IBS is based upon symptom criteria, consideration of patient demographics (that is, age, sex, race) and exclusion of organic disease. A thorough history specifically eliciting relevant family history, drug and dietary history is important as well as identification of psychosocial aspects.
Age is important for a correct diagnosis of irritable bowel syndrome; patients over the age of 50 with new bowel symptoms, especially those with a family history of colon cancer, should have this cancer excluded before concluding that they have irritable bowel syndrome.
In patients younger than 50 years, knowing the amount of milk consumed will strongly affect whether a diagnosis of lactose intolerance should be pursued.
Alarm symptoms requiring further investigations are:
1. Relevant abnormalities on physical examination
2. Documented weight loss
3. Nocturnal symptoms
4. Blood mixed in stools
5. History of antibiotic use
6. Family history of colon cancer
A thorough examination and targeted investigations are needed to exclude organic pathology. These include routine full blood count, erythrocyte sedimentation rate, biochemistry, and microbiology with examination of stool for ova, cysts and parasites.
PATHOGENESIS
The pathogenesis of IBS is multifactorial and in IBS patients a profound dysregulation of the brain gut axis takes place. In particular is more evident the relationship between stress and brain-gut-axis with the important role of CFR.
Many patients believe that stress induces symptoms. IBS is associated with an increased incidence of psychiatric disease. However, it has proved difficult to document a relationship between stress and abdominal symptoms on a daily basis.
Bacterial infection has recently been recognized as an important cause of IBS. Infections such as Campylobacter jejuni, Salmonella enteritidis and Shigella flexneri produce diarrhoea and abdominal pain which usually resolves rapidly. Patients with post-infectious IBS account for 6–17% of the IBS population, and typically have the diarrhoea-predominant subtype (D-IBS). Compared with patients with other types of IBS, they are less likely to have a history of psychiatric disease requiring treatment and have a better prognosis. In addition, release of important neuropeptides, changes in behaviour, motility, endocrine functions and microbiota occur.
Recently a role of immune system was also demonstrated.
Stress and the gut: pathophysiology, clinical consequences, diagnostic approach and treatment options, 2011
Role of corticotropin-releasing hormone in irritable bowel syndrome and intestinal inflammation, 2007
Irritable bowel syndrome - An inflammatory disease involving mast cells, 2011
Distinctive clinical, psychological, and histological features of postinfective irritable bowel syndrome, 2003
RISK FACTORS
Among important risk factors is genetic susceptibility and chronic stress (life events) while the key trigger factors include psychosocial factors and exposure of the gut to infections or overuse of antibiotics leading to negative alterations in gut flora.
The only significant predictor was a bacterial infection in the previous year. The relative risk of developing IBS within the following year was approximately 11 times greater than for those with no infection.
THERAPY
The therapy of IBS includes: general measures, pharmacotherapy and psychological and behavioural therapy.
Diet
A lot of patients believe that diet plays an important role in the exacerbation of symptoms. Dietary assessment plays important role, and the symptoms may improve after avoiding milk products, some carbohydrates such as sorbitol, mannitol (found in fruits and chewing gum), lactose (found in milk, chocolate, cream, cheese and yoghurt) and scodarose (found in onions), which can all cause diarrhoea, abdominal pain.
Excessive consumption of caffeine may also be responsible for diarrhoea through its direct stimulatory effect on the colon. Eventually screening for food intolerance or allergy should be performed, in fact patients with IBS have increate prevalence of lactose, fructose or sorbitol intolerance.
In a patient with constipation predominant IBS the traditional advice has been to adopt a high fibre diet. Increasing intake of a range of different dietary “fibres” including those from cereals, fruits, and vegetables have been shown to increase stool weight and accelerate gut transit.
Bile salt binding agents
A few patients with diarrhoea predominant IBS have bile salt malabsorption and may respond to cholestyramine. The tolerability of cholestyramine is poor with side effects such as constipation and diarrhoea, as well as nausea, vomiting, and gastrointestinal discomfort
5HT3 antagonists
Serotonin stored in enterochromaffin cells plays a crucial role in the motility and visceral sensitivity and stimulates intestinal secretion and propulsion acting through 5HT3 receptors. 5HT3 antagonists slow colonic transit, inhibit GI secretions and improve stool consistency
Enterochromaffin cells act as sensor cells that signal every luminal change (acidity, osmolarity, nutrients, pathogens, bacterially-derived toxins) by releasing 5-HT in the gut. The release of 5-HT that can occur constitutively and following stimulation activates nerves fibers, which besides affecting gut motility and the sensory response, can also cause the secretion of mucus from goblet cells and an increase in passive water flux to wash away any pathogens or noxious agents.
5HT3 antagonists slow colonic transit, inhibit GI secretions and improve stool consistency
Tricyclic antidepressants
They are widely used as an analgesic in a range of painful somatic disorders, including chronic back pain and trigeminal and diabetic neuralgias, often in combination with other drugs. In low
doses they are also successful in treating IBS.
Loperamide
Diarrhoea dominant IBS is associated with acceleration of small bowel and proximal colonic transit and responds to opioids. A drawback of opioid use is the tendency to induce constipation.
This μ-opioid agonist, which does not cross the blood–brain barrier, is generally well tolerated without the sedative or nauseating effects of codeine. It is extremely effective in controlling excessive bowel frequency but less so in reducing abdominal pain, and may aggravate bloating. Treatment should be started at 2 mg per day, increasing to a maximum of 16 mg daily.
Loperamide in treatment of irritable bowel syndrome--a double-blind placebo controlled study, 1987
Antispasmodics
These drugs, which inhibit smooth muscle contractions have a beneficial effect on abdominal pain.
Probiotics
Recently, an increasing number of studies indicates the positive effect of probiotics on IBS symptoms. The postulated mechanisms of action of probiotics on stressed gastrointestinal mucosa include improvement of the barrier function of the epithelium (permeability), suppression of the growth and binding of pathogenic bacteria, positive effect on visceral hypersensitivity and immunomodulatory effect (inhibition of subclinical inflammation in IBS). Despite the high number of studies using probiotics in IBS patients, a lot of new questions have been left unanswered such as the optimal dose, its role in combination therapy, strain specific activity, stability within GI tract, possible development of antibiotic resistance and the duration of therapy. Probiotics may vary in species, strains, preparation and doses, what makes the interpretation of the efficacy difficult. To answer all these questions, large placebo controlled trials are needed in the future.
Other
Complementary or alternative approaches includes cognitive behavioural therapy (CBT), dynamic psychotherapy, stress management, hypnotherapy, relaxation therapy and even acupuncture represent further important treatment approaches to reduce the symptoms of IBS.
Management of irritable bowel syndrome (IBS) in adults: conventional and complementary/alternative approaches, 2011
