definition: A functional motility illness of the small and large intestines, in the absence of true structural damage to the intestines.
etiology: IBS consists of various degrees of constipation, diarrhea and abdominal pain, usually presenting as a reaction to stress in a susceptible patient.
This is the most common gastrointestinal disease seen by general practitioners, covering about 30-50% of their referrals to gastroenterologists. Patients present in one of three ways: with spastic colitis causing pain and constipation; with chronic watery diarrhea showing high levels of mucus; or with abdominal pain and alternating constipation and diarrhea.
In IBS no anatomic defect can be found: the basic pathophysiologic abnormality is a change in stability of the small and large bowel motility. In patients with the spastic colon presentation, there is a measurable increase in resting colonic peristalsis; in patients whose chief complaint is diarrhea, there is a measurable decrease in intestinal motility. Precipitating and aggravating factors surrounding the onset and maintenance of the disorder include diet, drugs, hormones or, especially, emotional stresses such as depression, hysteria, obsessive-compulsive traits, anxiety and resentment. Common psychosocial situations associated with IBS are marital discord, death of a loved one, worrying over children or job, or just excessive anxiety over everyday matters. IBS is a disease predominantly of women (3:1 to men), and the average age of onset is 20-40.
It is most likely to be a disorder of synergistic nature, that is, a series of triggers which individually would not provoke an outbreak may do so when combined. In this regard, food sensitivities, bowel flora imbalance and colonic malfermentation are likely to play a significant role: for example, emotional or stress triggers which might affect the GI system only slightly tip over into IBS when the presence of offending foods or imbalanced flora create gastrointestinal reaction and instability. (King TS, et al. Lancet 1998 Oct 10;352(9135):1187-1189.)
signs and symptoms
Signs and symptoms vary based on the type of IBS the patient is experiencing.
spastic colon: The patient will complain of irregular, cramping, lower abdominal pain (usually over the sigmoid colon) and constipation, or alternating constipation and diarrhea: either way there is an excess of mucorrhea. The patient will also usually complain of excessive gas and bloating, although the bloating may not be apparent during physical exam.
general symptoms include heartburn, fatigue, headache, faintness, back pain, palpitations, and weakness
occasionally the pain of IBS may present as RUQ pain, necessitating a further investigation of peptic ulcer and/or biliary tract disease
Patients may also present with chronic watery diarrhea. It may have been going on sporadically for months or even years. It is usually morning diarrhea, occurring after awakening or after breakfast. Usually, the patient has 3-4 loose stools in the morning and thenormal stools for the rest of the day: it is rare for the patient to continue to have diarrhea throughout the day or at night. A variation to watery diarrhea is "pencil-thin" pasty stools.
Physical exam of any IBS patient is usually unremarkable except for evident anxiety in the patient. The abdomen may be distended if there is intense pain, but no rigidity or visible peristalsis will be noticeable. The lower left quadrant may contain palpable feces, although the rectal ampulla is empty of stool. The sigmoidoscopic exam is normal except for the preponderance of mucus and possible hyperemia that might be encountered.
lab findings:
stools must be carefully cultured for ova, parasites, and occult blood
barium enema usually unremarkable except for exaggerated haustra in constipated patients
(+) tests for food sensitivities
all other tests are normal
With the exclusion of of any other disease process, and the typical presentation of chronic, intermittent attacks of symptoms related to environmental and/or emotional stress, the diagnosis of IBS can be made.
course and prognosis
The disorder does not lead to serious disease such as inflammatory bowel disease or malignancy (although there might be an association between IBS and the development of diverticular disease). Determination of aggravating factors can yield good results, where those stressors prove controllable.
Spasmolytic drugs are sometimes given conventionally, but do not cure the condition and tend to constipate.
differential diagnosis
dietary abuses of irritating foods: coffee, tea, simple sugars, carbonated beverages, highly spiced foods
lactose or gluten intolerance
inflammatory bowel disease
food poisoning
intestinal infestation: giardiasis, amebiasis, etc.
intestinal candidiasis or other intestinal flora imbalance
cancer of the bowel
diverticulitis
laxative abuse
pancreatic insufficiency or another malabsorption disease
metabolic disorders such as diabetes mellitus, adrenal insufficiency, and hyperthyroidism
mechanical problem such as fecal impaction
footnotes
King TS, Elia M, Hunter JO. Abnormal colonic fermentation in irritable bowel syndrome. Lancet 1998 Oct 10;352(9135):1187-1189.
Abstract: BACKGROUND: The cause of irritable bowel syndrome (IBS) is unknown. It may follow gastroenteritis and be associated with an abnormal gut flora and with food intolerance. Our study was designed to assess whether these factors were associated with colonic malfermentation. METHODS: We carried out a crossover controlled trial of a standard diet and an exclusion diet matched for macronutrients in six female IBS patients and six female controls. During the final 72 h on each diet, faecal excretion of fat, nitrogen, starch, and non-starch polysaccharide NSP was measured, and total excretion of hydrogen and methane collected over 24 h in a purpose-built 1.4 m3 whole-body calorimeter. Breath hydrogen and methane excretion were then measured for 3 h after 20 g oral lactulose. FINDINGS: The maximum rate of gas excretion was significantly greater in patients than in controls (2.4 mL/min IQR 1.7-2.6 vs 0.6, 0.4-1.1). Although total gas production in patients was not greater than in controls (median 527 mL/24 h IQR 387-660 vs 412, 234-507), hydrogen production was higher (332, 318-478 vs 162, 126-217, p=0.009). In patients, the exclusion diet reduced symptoms and produced a fall in maximum gas excretion (0.5 mL/min IQR 0.3-0.7). After lactulose, breath hydrogen was greater on the standard than on the exclusion diet. INTERPRETATION: Colonic-gas production, particularly of hydrogen, is greater in patients with IBS than in controls, and both symptoms and gas production are reduced by an exclusion diet. This reduction may be associated with alterations in the activity of hydrogen-consuming bacteria. Fermentation may be an important factor in the pathogenesis of IBS.