Making a Positive Diagnosis of IBS
IBS is not associated with any definitive biochemical, structural, or serologic abnormalities that define its presence. The hallmark feature of IBS is abdominal pain or discomfort associated with altered bowel habits, and, often, the abdominal pain prompts patients to seek medical care. Because the symptoms of IBS are common to a number of other GI conditions, IBS was long considered a "diagnosis of exclusion," leading to excessive testing of patients with characteristic symptoms. Fortunately, advances in research have led to the development of symptom-based approaches, aimed at standardizing IBS patient subgroups, and the development of consensus guidelines advocating a positive diagnosis of IBS based primarily on the pattern and nature of symptoms, without the need for excessive laboratory testing.[2,15]
In 1978, Manning and colleagues[16,17,18] proposed diagnostic criteria for IBS that were found to be reasonably sensitive and specific. More recently, an international group of experts in functional GI motility disorders convened to develop symptom-based criteria, known as the Rome criteria (Rome I, Rome II, and Rome III[20,21]), to better define and provide tools by which a positive diagnosis of these disorders could be made. The Rome I criteria for IBS were shown to be sensitive and specific.[22,23] The Rome II criteria, published in 1999, were intended to simplify the more complex Rome I criteria by better defining the nonconsecutive, multisymptom nature of this disorder. Clinical studies validating the Rome II criteria are beginning to emerge. Consensus has not yet been reached regarding which of the Rome criteria are more sensitive for identifying IBS patients in clinical practice[22,24,25] and which of the 2 more accurately estimates the prevalence of IBS.[17,26,27] A recent US population-based follow-up study found that the Rome II criteria were limited in capturing the fluctuating nature of IBS. Over a 2-year period, patients experienced symptoms episodically, including abdominal pain; the absence of pain at time of follow-up excluded many patients from meeting IBS criteria. Overall, the Rome I and II criteria are considered useful for standardizing enrollment of patients into clinical trials. However, many clinicians believe that these criteria are too restrictive for use in clinical practice. The American College of Gastroenterology (ACG) Functional GI Disorders Task Force suggests using a broader definition of IBS: abdominal discomfort associated with altered bowel habits. The Rome III working team met in the fall of 2004; updated criteria were published in April 2006. The principle difference between Rome III guidelines as compared with the Rome II criteria lies in the less restrictive timeframe for symptoms. Whereas the Rome II criteria require symptoms to be present for at least 12 weeks (not necessarily consecutive) in the past 12 months, the Rome III criteria require symptoms to originate for 6 months prior to diagnosis, and be currently active (ie, patient meets criteria) for 3 months. The categorization of IBS patients into the constipation, diarrhea, or mixed subtypes has also been revised (based on stool consistency). It is hoped that the less restrictive symptom timeframe requirements of the Rome III guidelines will make them more clinically practical than the previous iterations.
The Rome III criteria, in conjunction with careful history-taking (medical, family, and medication) and thorough physical examination, can be applied as part of the stepwise, symptom-based approach to diagnosing IBS (Figure). The presence of alarm features (eg, rectal bleeding, history of colon cancer or inflammatory bowel disease) potentially indicative of organic disease necessitates further evaluation.
Until recently, the role of diagnostic testing in diagnosing IBS was a topic of continuing debate. Recent evidence indicates that when a patient meets the Rome criteria, and has no features suggestive of organic disease, the pretest probability of making an accurate diagnosis of IBS based primarily on symptoms is high. In a systematic review conducted by Cash and colleagues, the pretest probability of inflammatory bowel disease, colorectal cancer, or infectious diarrhea was found to be less than 1% in patients meeting symptom-based criteria for IBS. Extensive diagnostic testing rarely identifies organic GI disease in these patients. However, one exception is celiac disease: the pretest probability of celiac disease in patients meeting symptom-based criteria for IBS was 10 times higher than that in the general population. Recently, testing for celiac disease in patients with suspected IBS with diarrhea (IBS-D) has been shown to be most financially feasible in areas in which the prevalence of celiac disease is at least 8%. These findings were supported by the evidence-based recommendation made by the ACG Functional GI Disorders Task Force, whereby they concluded that there is insufficient evidence to recommend the routine performance of diagnostic testing in patients who meet symptom-based criteria for IBS (eg, Manning, Rome I, Rome II) -- therefore, supporting a symptom-based approach to making a positive diagnosis of IBS.
The extent to which this guidance is implemented into clinical practice is based on clinical judgment and experience of the physicians. Most physicians agree that standard laboratory testing, such as complete cell blood count, chemistry panel, and erythrocyte sedimentation rate, should be performed in patients with symptoms of IBS. However, if these studies have been performed recently, after symptoms emerged, there is no need to repeat them. For a patient with IBS symptoms and no comorbid conditions, test results should all be within normal limits. Colonoscopy is generally not required in the absence of features indicative of organic disease (eg, family history of colon cancer), although it should be performed in individuals older than 50 years of age. However, as mentioned previously, if the patient (regardless of age) underwent colonoscopy after the development of symptoms, a repeat test is not warranted. In addition to routine laboratory testing, thyroid function studies, ova and parasite examination, urinalysis, and breath tests for lactose intolerance may be considered. Globally, however, the value of diagnostic testing in IBS has not been established in patients who meet symptom-based criteria for IBS and who do not have symptoms indicative of organic disease; additional diagnostic testing does not increase the probability of detecting organic disease and does not alter the diagnosis of IBS once it is made.[32,34,35,36]
A symptom-based diagnosis of IBS is durable. In a longitudinal study in which 75 patients were reevaluated 10 to 13 years after an initial IBS diagnosis, all patients still met the diagnostic criteria for IBS (Manning, Rome I, Rome II) and few had received an alternative diagnosis during that period. In other studies with follow-up periods ranging from 3 to 5 years, development of organic disease occurred in less than 7% of patients initially given a diagnosis of IBS using the symptom-based approach.
Historically IBS was considered a diagnosis by exclusion and was viewed as a purely psychosomatic condition. Within the past 2 decades, however, symptom-based diagnostic criteria have been established that allow physicians to positively and confidently diagnose IBS.
© 2006 Medscape
Cite this: IBS -- Review and What's New - Medscape - Jul 26, 2006.