This is a chronic gastrointestinal disorder caused by functional defects and characterized by abdominal pain and change in bowel habits. It affects about 26-33% of the Nigerian population, about 17% of the UK population and about 14% of the population. It is more common in adolescents and young adults and more likely to develop in women than men.

CAUSES

The hallmark of IBS is the absence of a specific structural or organic cause of dysfunction. The functional defects linked to IBS have been identified as a three-part complex consisting of:

• Change in GI motility due to an alteration in the electrical activity of the gastrointestinal muscles. This leads primarily to altered transit time of meals causing constipation or diarrhea, depending on what the patient is prone to.
• Visceral hyperalgesia simply describes the exaggerated perception of normal GI motility and visceral pain hence patients tend to feel widespread pain across the abdomen.
• Psychopathology, which although has no clear association with IBS, is suggested because patients with IBS are noted to have a higher incidence of mental disorders than others.

Infection with organisms such as Giardia lamblia increases the risk of developing IBS. The limbic system in the brain which mediates autonomic responses also affects bowel motility to varying degrees in IBS patients.

Areas of inflammation and presence of inflammatory cells have been noticed in the intestines of some patients. Alteration in the normal flora of the intestines and increased intestinal permeability (especially in diarrhoea-prone IBS) are also implicated mechanisms for some symptoms that occur.

Patients with IBS also tend to experience intolerance to foods containing lipids and certain carbohydrates.

SIGNS AND SYMPTOMS

About 50% of patients experience symptoms before the age of 35. Symptoms include:

• Change in bowel habits: this can vary from constipation to diarrhoea or a mix of both in different patients
• Abdominal pain: usually diffuse, can be acute and sharp, may be precipitated by meals and improved by defecation.
• Abdominal bloating/distension
• Others are excess discharge of mucus, nausea, vomiting, abdominal discomfort. Sexual dysfunction and urinary urgency have also been noted.

DIAGNOSIS

This requires a detailed history and examination. The Rome IV diagnostic criteria is used to make diagnosis and this requires presence of recurrent abdominal pain for at least 1 day per week over the previous 3 months associated with 2 or more of;

Relation to defecation

Association with a change in stool frequency

Association with a change in stool form or appearance.

Other symptoms may also be present.

Four patterns of symptoms may be seen, these are:

-IBS-D (diarrhea predominant)

-IBS-C (constipation predominant)

-IBS-M (mixed diarrhea and constipation)

-IBS-U (unclassified).

Patterns however are not specific as sub types change in patients.

Although the 2009 American College of Gastroenterologists doesn’t recommend laboratory tests or diagnostic imaging in patients under the age of 50 who have symptoms of IBS, it is important to investigate thoroughly if symptoms such as weight loss, anaemia and family history of GI disorders (e.g. colorectal cancer, inflammatory bowel disease etc.) occur.

Laboratory tests typically done for diagnosis include:

• Full blood count: to detect anaemia and infections
• Electrolytes, Urea and Creatinine assays: especially in IBS-D patients to rule out dehydration
• Stool microscopy, culture and sensitivity: to detect presence of parasites and/or ova
• Electrolyte sedimentation rate and C-reactive protein: to detect inflammation

Tests done to rule out other diagnoses include Thyroid function tests for hyperthyroidism or hypothyroidism, Hydrogen breath test for Lactose intolerance (Dietary studies done by incorporating a lactose-free diet for a week may also help), Tissue transglutamine antibody testing and Small bowel biopsy for Celiac disease.

Abdominal Computed Tomography and Magnetic Resonance Imaging scans can be done if tumours are suspected and Colonoscopy is important in patients over the age of 50 and younger patients with warning signs.

TREATMENT

This is individualized and consists mainly of psychological support and dietary modifications. In recent years, IBS agents e.g. Linaclotide, Alosetron, Lubiprostone etc. have been approved, enhancing treatment of symptoms. Adjunct pharmacological therapy may also be needed e.g. prebiotics, anti-diarrheal agents (e.g. loperamide), anti-depressants etc. Patient counselling is required, chronicity of disorder and normal life expectancy are to be emphasized and stressors are to be identified and avoided.

Sources: Medscape, NHS, BMJ journals