Functional Gastrointestinal Disorders: Novel Insights and Treatments

, Mayo Clinic and Mayo Foundation, Rochester, Minn.


Medscape General Medicine. 1999;1(3) 

In This Article

Functional Bowel Disorders: Definition and Impact

A functional gastrointestinal disorder comprises symptoms arising in the mid or lower gastrointestinal tract that are not attributable to anatomic or biochemical defects.[4,5,6] The symptoms include abdominal pain, early satiety, nausea, bloating, distention, and various symptoms of disordered defecation. The 3 most common functional bowel disorders are irritable bowel syndrome (IBS), constipation, and functional dyspepsia.

IBS, the most common functional bowel disorder, is characterized by chronic or recurrent symptoms of lower abdominal pain related to bowel movements, change in bowel habit (diarrhea, constipation, or alternating), a sense of incomplete rectal evacuation, passage of mucus with stool, and abdominal bloating and distention.[5,6,7] The prevalence of this disorder in most countries is approximately 10%.

Constipation is defined in many ways and perceived very differently among patients.[8] It is clear that a frequency definition of constipation is insufficient, although a bowel movement frequency of less than 1 every 3 days is generally regarded as being outside the normal range. However, most patients perceive that they are constipated when they have to strain excessively or have difficulty passing stool from the rectum or completing the evacuation of stool. With such a variety of definitions, the prevalence of constipation in the community is difficult to ascertain, with estimates ranging from 3% to 20%.[9] There is increasing evidence that a considerable proportion (perhaps as high as 50% in tertiary centers) of patients with constipation have a disorder of the process of rectal evacuation.[10] Normal defecation[2] requires coordination of colonic contractions, volitional rise in intra-abdominal pressure, and relaxation of the pelvic floor and anal sphincters (see Figure 1).

Figure 1. Functional gastrointestinal disorders: biopsychosocial disorders of high prevalence and impact. Hp=Helicobacter pylori; QOL=quality of life; HAPCs= high-amplitude, rapidly propagated colonic contractions; S2, 3, 4=sacral roots 2, 3, and 4

Functional dyspepsia is also a common problem (prevalence estimated at 20% in a US community),[12] and this disorder is characterized by chronic or recurrent symptoms of upper abdominal pain or "discomfort," which is a summary term for such symptoms as early satiety, nausea, bloating, and vomiting.[5,11]

In IBS, functional dyspepsia, and constipation, no structural or biochemical abnormalities are identified. Around 30% of patients with IBS have symptoms consistent with functional dyspepsia, either concurrently or at other times.[12,13]

There is also overlap in the clinical symptomatology of patients with constipation-predominant IBS and those who have constipation that results from an evacuation disorder. In patients with suspected IBS, careful evaluation of the dynamics of defecation is essential in order to exclude a disorder of rectal evacuation, to provide the best treatment, and to avoid greater direct and indirect costs resulting from mismanagement.

Societal and Economic Impact

One of the most important societal perspectives resulting from functional bowel disorders is the degree of absenteeism that is recorded among patients with these conditions.[13] For example, it has been estimated that patients with IBS recorded work or school absences of up to 13 days per year compared with a control population, who reported 5 days of absence per year.[13] This level of absenteeism is equivalent to that associated with the common cold and flu and presents a significant burden to any nation's economy. Indeed, it is estimated that 0.1%[14] to 0.5%[15] of healthcare expenditures in industrialized countries are attributable to IBS, and that 66% to 75% of all the economic burden from functional gastrointestinal disorders results from indirect costs secondary to loss of days at work or school.[15]

Functional bowel disorders constitute a significant economic burden in the form of direct costs. It has been estimated that annual charges for healthcare delivery for IBS in the United States are around $8 billion.[16] More recently, however, the annual costs incurred by 8 major industrialized countries were estimated at approximately $41 billion, including $25 billion in the United States and over $4 billion each in Japan and Germany.[15]