Irritable bowel syndrome (IBS) is a functional bowel disorder in which recurrent abdominal pain and/or discomfort is associated with a change in bowel habit [1
]. The diagnosis of IBS is currently based on the Rome III symptom-based criteria for IBS (Box 1
). IBS is subtyped, based on predominant bowel habit: IBS with constipation (IBS-C), diarrhea (IBS-D) and mixed pattern (IBS-M). The subtype classifications are based on the prevalence of altered stool form (i.e., loose/watery stool and/or hard/lumpy stool) (Box 2
]. Individuals who are classified as not fitting IBS-D or IBS-C subtypes are classified as either IBS-M or IBS-A. IBS-M is preferred for individuals for whom both diarrhea and constipation-type stool form 25% or more of their bowel movements. The IBS-A subtype is now used in cases where an individual’s bowel habits transitions between IBS-C and IBS-D over time. In this review, IBS-M and IBS-A will be referred to as IBS-M/A. Supportive symptoms of IBS include change in frequency of stool, abnormal stool form, straining with defecation, urgency, feeling of incomplete defecation, passage of mucus and bloating.
Box 1. Rome III criteria for the diagnosis of irritable bowel syndrome
Recurrent abdominal pain or discomfort* for at least 3 days per month in the last 3 months that is associated with two or more of the following:
- Improvement with defecation
- Onset associated with a change in stool frequency
- Onset associated with change in stool form (appearance)
*Discomfort means an uncomfortable sensation not described as pain. Symptom onset at least 6 months prior to diagnosis.
Box 2. Subtypes of irritable bowel syndrome based on predominant stool pattern
IBS with constipation (IBS-C)
- Hard or lumpy stools ≥25% and loose (mushy) or watery stools <25% of bowel movements
IBS with diarrhea (IBS-D)
- Loose (mushy) or watery stools ≥25% and hard or lumpy stools <25% of bowel movements
Mixed IBS (IBS-M)
- Hard or lumpy stools ≥25% and loose (mushy) or watery stools ≥25% of bowel movements
- Insufficient abnormality of stool consistency to meet criteria for IBS-C, IBS-D or IBS-M
IBS: Irritable bowel syndrome.
The estimated prevalence of IBS in Western countries is 7–15% [2
]. There is a 2–2.5:1 ratio of women to men who seek healthcare services for IBS, although the female predominance is less in the general population. Symptoms of IBS greatly impact the health-related quality of life (HRQOL) of affected individuals and is associated with a significant healthcare and economic burden. Several studies have found that individuals with IBS have a significantly diminished HRQOL when compared with the general population, and it is lower or comparable to patients with other chronic illnesses [7
]. The economic impact of IBS on society is significant, with annual direct costs estimated at US$1.35 billion and indirect costs of at least $200 million [1
]. Treatment of IBS is comprised of a multicomponent approach, although it is commonly targeted towards the predominant subtype and/or other symptoms, such as abdominal pain/discomfort and bloating.
Several studies have reported that women have a higher prevalence of pain [11
], bloating and distension [12
] and hard or lumpy stools [16
] than men. Women are more likely than men to be classified into the IBS-C subtype [17
]. In addition, it appears that female sex is a risk factor for the development of postinfectious IBS, which occurs in a subset of individuals who develop IBS-like symptoms after an enteric infection [18
]. Women with IBS report greater IBS severity [14
], greater impact of symptoms on daily life and lower HRQOL [19
] than men with IBS. There is also some evidence suggesting that women with IBS respond differently to pharmacologic and psychological treatment compared with their male counterparts [23
]. The reasons for sex- and gender-related differences in the prevalence, symptom presentation, pathophysiology and treatment response are not well understood. Explanations include differences in pain sensation, cognitive response to pain, reporting bias, gender role and fluctuation in ovarian hormones [28
This article will review current and emerging therapies for IBS and will also highlight sex and gender differences in clinical trials and treatment response if present.