A diagnosis is based on identifying positive symptoms (e.g., Rome criteria) consistent with the condition (see Table 1 below), and excluding other conditions with similar clinical presentations in a cost-effective manner.
Table 1: Rome II Diagnostic Criteria for Irritable Bowel Syndrome (IBS)
At least 12 weeks, which need not be consecutive, in the preceding 12 months of abdominal discomfort or pain that has 2 of 3 features:
- Relieved with defecation
- Onset associated with a change in frequency of stool
- Onset associated with a change in form (appearance) of stool
Symptoms that cumulatively support the diagnosis of IBS:
- Abnormal stool frequency (for research purposes, "abnormal" may be defined as greater than three bowel movements per day and less than three bowel movements per week)
- Abnormal stool form (lumpy/hard or loose/watery stool)
- Abnormal stool passage (straining, urgency, or feeling of incomplete evacuation)
- Passage of mucus
- Bloating or feeling of abdominal distension
The diagnosis of a functional bowel disorder always presumes the absence of a structural or biochemical explanation for the symptoms.
Physical Examination and Investigations
A medical history and physical examination, and certain routine studies, are recommended to assess the presence of "alarm signs" or "red flags" (fever, weight loss, blood in stools, anemia, abnormal physical findings or blood studies, family history of irritable bowel disorders or cancer) that might require more extensive evaluation.
For screening purposes, a stool Hemoccult and complete blood count are recommended. A sedimentation rate (more so in younger patients), serum chemistries and albumin, and stool for ova and parasites can be ordered based on symptom pattern, geographic area, and relevant clinical features (e.g., predominant diarrhea, areas of endemic infection). A colonoscopy is recommended for patients over age 50 years (due to higher pretest probability of colon cancer), but in younger patients, performing a colonoscopy or sigmoidoscopy is determined by clinical features suggestive of disease (e.g., diarrhea, weight loss) and may not be indicated.
Other diagnostic studies will depend on the symptom subtype. For example, for constipation-predominant symptoms, a therapeutic trial of fiber may be sufficient. However, if symptoms are persistent, confirmation of slow colonic transit with a whole gut transit test or evaluation for obstructed defecation with anorectal motility or defecating proctography may be indicated. For diarrhea-predominant symptoms, clinical judgment will determine the choice of studies. Particularly for loose/watery stools, a lactose/dextrose H2 breath test and serologies for celiac sprue or small bowel (for giardia, small bowel malabsorption) or colonic (for microscopic colitis) biopsies may be indicated. However, controversy exists about the threshold for ordering these tests, given limited evidence as to their sensitivity, specificity, and cost utility. If negative, a therapeutic trial of loperamide can be ordered. For patients with pain as the predominant symptom, a plain abdominal radiography during an acute episode to exclude bowel obstruction and other abdominal pathology is recommended. If negative, a therapeutic trial of an antispasmodic can be ordered. Further imaging studies (e.g., small bowel series, computerized tomography scan) of the bowel and other evaluation strategies may be modified based on the duration and severity of symptoms, changes in symptom type, or severity over time and demographic or psychosocial factors.
Treatment can then be started and the patient’s condition reevaluated in 3-6 weeks. If treatment is unsuccessful, or if further evaluation seems needed, additional studies based on symptom subtype can then be undertaken.
The treatment strategy is based on the nature and severity of the symptoms, the characteristics and degree of functional impairment, and the presence of psychosocial difficulties affecting the course of the illness. Patients with mild symptoms usually respond to education, reassurance, and simple treatments not requiring prescription medication. A smaller group of patients with moderate symptoms have more disability and require pharmacological treatments directed at altered gut physiology or psychological treatments. The very small proportion of patients with severe and refractory symptoms are frequently seen at referral centers and have more constant pain and psychosocial disablement. They may benefit from antidepressant treatment, psychological treatments and support, and in occasional cases, referral to a multidisciplinary pain center.
Components of the Treatment Strategy
- General treatment approach
For all patients, the physician should establish an effective therapeutic relationship, provide patient education and reassurance, and help with dietary and lifestyle modifications when needed. Symptom monitoring using a diary may help identify possible triggers to symptom exacerbation and may guide choices for psychological and other treatments.
- Medication directed at the predominant symptom(s)
For abdominal pain, consider antispasmodic (anticholinergic) medication, particularly when symptoms are exacerbated by meals, or a tricyclic antidepressant (TCA), particularly if pain is frequent or severe (see below). For constipation, increased dietary fiber (25 g/day) is recommended for simple constipation, although evidence of its effectiveness in reducing pain is mixed. For diarrhea, loperamide (2-4 mg, up to four times daily) can reduce loose stools, urgency, and fecal soiling. Cholestyramine may be considered for patients with cholecystectomy or who may have idiopathic bile acid malabsorption. Newly released agents acting at the 5-HT receptor may help painful symptoms, and must be used based on whether the stool habit is primarily diarrhea (e.g., alosetron) or constipation (e.g., tegaserod). No data exist as to the role in mixed or alternating IBS, and recommendations as to their use as first or second line treatments need to be determined based on issues of efficacy, safety, and cost. Other receptor active agents for IBS are currently under active investigation.
- Psychological treatments
Psychological treatments are initiated when symptoms are severe enough to impair health-related quality of life. Mental health referral may also be made for treatment of associated psychiatric disorders such as major depression or a history of abuse that interferes with adjustment to illness. To enhance patient motivation, the physician needs to explain that along with the primary care physician, the mental health professional is part of the treatment team involved in the overall plan of care.
Cognitive-behavioral treatment, dynamic (interpersonal) psychotherapy, hypnosis, and stress management/relaxation seem to be effective in reducing abdominal pain and diarrhea (but not constipation), and also reduce anxiety and other psychological symptoms. Improvement may relate to changes in GI physiology, improved coping strategies, or in the interpretation of enteroceptive signals from the gut. Greater benefit may be expected in patients who relate symptom exacerbations to stressors, have associated symptoms of anxiety or depression, or have symptoms of a relatively short duration, and have a waxing and waning of symptoms rather than chronic pain. No one psychological treatment seems superior, and future studies need to determine the relative efficacy of these treatments for various subgroups of patients.
- Centrally acting medications
Antidepressants are recommended for moderate to severe symptoms of pain and may be helpful for less severe symptoms. They have neuromodulatory and analgesic properties independent of their psychotropic effect and alter GI physiology (e.g., visceral sensitivity, motility, and secretion). In general, these benefits occur sooner and in lower dosages than when prescribed for treatment of major depression. Most studies showing benefit have evaluated TCAs (e.g., amitriptyline, desipramine), rather than selective serotonin reuptake inhibitors (SSRIs) (e.g., fluoxetine, paroxetine, sertraline) in IBS, and no comparative studies have been done. However, SSRIs are in use, particularly for patients with comorbid psychiatric (e.g., anxiety-related) disorders, and they have low side effect profiles and better safety than the TCAs. Anxiolytics are generally not recommended because of weak treatment effects, a potential for physical dependence, and interaction with other drugs and alcohol.