Irritable Bowel Syndrome


IBS has a worldwide prevalence rate of 5%–20% , and makes up ~25% of “functional gastrointestinal disorders” diagnoses. Functional abdominal pain is difficult to define, diffuse (not localized), and not associated with structural or biochemical changes. IBS, specifically, is characterized by chronic abdominal pain, altered bowel habits (diarrhea or constipation), and the absence of any alarm findings. The pain and symptoms of IBS often last a lifetime and have a significant impact on quality of life (QOL). A meta-analysis of 18 studies from the United States and the United Kingdom calculated the annual direct cost of each IBS patient (drugs, procedures, and doctors visits) to be $348–$8750 and the annual indirect cost (loss of work days and decreased productivity) to be $355–$3444. , Within the United States, IBS has an annual direct cost of $228 million in doctors’ visits and $80 million in drugs. IBS patients are significant utilizers of the healthcare system. It is estimated that IBS cases make up 25%–50% of the annual referrals seen by a gastroenterologist. , In short, IBS has a significant impact on healthcare utilization, the global economy, and on patients’ QOL. It is worth understanding how to diagnose and manage this syndrome’s hallmark feature – abdominal pain.

Etiology and Pathogenesis

The chronic abdominal pain of IBS, like most chronic pain, is multidimensional (peripheral sensory, affective emotional, and cognitive central nervous system) and multifactorial, including changes in physiology at the peripheral and central level. Signals from the colon are conveyed to the spinal cord through first and second-order neurons and then travel to the brain via the spinothalamic, spinoreticular, and spinomesencephalic pathways. These tracts then project to the somatosensory cortex, which functions to discriminate the location of painful signals, whether they are somatic or visceral in origin. These tracts also project to the perigenual anterior cingulate cortex and midcingulate cortex within the limbic system. , These areas of the limbic system function in the regulation and handling of pain affect as well as behavioral response modification.

It is believed that the central feature of functional gastrointestinal disorders (FGID), like IBS, is a change within the central nervous system’s modulation and processing of painful peripheral signals. There may also be an abnormal or increased peripheral signal originating from the gut. Changes at the peripheral level may be due to food, stress, visceral inflammation, menses, previous surgery, or acute gastrointestinal infection. , This enhanced peripheral signal can be further accentuated by spinal or central level hyperexcitability – leading to a state of visceral hyperalgesia (exaggerated sense of pain) or allodynia (pain that results from a nonnoxious stimulus) in IBS patients. , Heightened peripheral sensitivity has a role at the beginning of the IBS pain process. It is the CNS, however, not the periphery that leads to chronic pain in IBS patients. Central regulation, not peripheral sensitivity, is the primary factor in chronic pain related to IBS. Patients with psychiatric disease, significant life stress, sexual or physical trauma, poor relational support, and poor coping skills demonstrate more severe and more chronic pain, as well as poorer health outcomes.

Clinical Features

IBS is characterized by chronic abdominal pain and altered bowel habits. The chronic abdominal pain of IBS is usually “crampy” in nature with varying intensity and intermittent exacerbations. Severity can range from mild and episodic pain to severe and unrelenting. , , The pain is typically related to defecation; sometimes relieved with defecation, sometimes exacerbated by it. Stress and food commonly worsen the pain. A bloated sensation and frequent flatulence or belching are other common associated symptoms.

A patient’s description of their pain can be a valuable insight into the origin or components of a multifactorial etiology. A “nauseating,” “sharp,” or “stabbing” description is consistent with a strong emotional component and therefore limbic origin. “Constant” and not affected by eating or defecation is unlikely to be associated with an abnormality in GI motility. When a patient describes their abdominal pain, and it is couched amidst several other pain complaints, there is likely a component of central sensitization. When the patient’s abdominal pain is part of a series of pains over their lifetime, the clinician has to be concerned for impaired limbic modulation as a preeminent factor.

IBS is as much behavioral as it is symptomatic, but IBS cannot be diagnosed by behavioral changes alone. It is important to evaluate the patient’s cognitive and emotional patterns from a biopsychosocial model – recognizing that a patient’s behavior reflects how they are evaluating, reacting to, and handling their symptoms. Many behaviors are maladaptive and present an opportunity for the clinician to intervene and counsel healthier, more effective habits. It is not uncommon to discover concurrent psychiatric comorbidities, “unresolved loss, a history of abuse, poor social support, and maladaptive coping skills.” Referral to a mental health professional can be of great value, and help in the amelioration of a patient’s symptoms. Additionally, a trusting and therapeutic relationship can be an avenue by which more healthful habits are fostered.


There are no diagnostic biomarkers specific for IBS; it is a clinical diagnosis of exclusion. It is this workup process that contributes to the heavy health care utilization and economic burden previously described. While many physicians may not feel comfortable without first completing a thorough workup, other etiologies should be investigated only as directed by history and physical exam findings. , The Rome Foundation Criteria is the current standard for diagnosing FGIDs and IBS. It builds and expands on the original Manning criteria and incorporates a combination of symptoms to increase the sensitivity and specificity to diagnose IBS. The latest version, the Rome IV criteria, was published in May 2016 ( Table 19.1 ). , , ,

Table 19.1

Rome IV Criteria for Diagnosis of IBS

Presence of recurrent abdominal pain, on average at least 1 day/week in the last 3 months, with symptom onset at least 6 months before diagnosis, with 2 of the 3 below criteria:

  • Abdominal pain related to defecation (either increasing or decreasing the pain)

  • Associated with a change in stool frequency

  • Associated with a change in stool appearance

For the diagnosis of IBS, Rome IV requires:

  • the presence of recurrent abdominal pain

  • on average at least 1 day/week in the last 3 months

  • with symptom onset at least 6 months before diagnosis

Additionally, the pain must be associated with at least two of the three following symptoms:

  • (1)

    Related to defecation (either increasing or decreasing the pain)

  • (2)

    Associated with a change in stool frequency

  • (3)

    Associated with a change in stool appearance

“Alarm” or “red flag symptoms” must be absent. These include unintended weight loss, blood in the stool, nocturnal symptoms, fever, family history of serious gastrointestinal disease (e.g., colorectal cancer, inflammatory bowel disease, or celiac disease), new onset of IBS symptoms after age 50, or an abnormal finding on physical exam. A complete blood count, c-reactive protein, and celiac panel are high yield, relatively low cost, and commonly recommended as part of the routine, initial evaluation. , A thyroid panel, fecal calprotectin, and stool analysis can also be considered based on history and physical exam. Again, patients with a clinical presentation consistent with the Rome criteria, who lack any red flags on H&P, warrant only a basic evaluation — after which the clinician can feel comfortable making a diagnosis of IBS. ,

Physical Exam Findings

The purpose of the physical exam should be to allay patient anxiety, to meet patient expectations, and to rule out organic disease.

Abdominal Exam

  • The clinician should palpate for internal changes such as an enlarged liver, abdominal mass, or signs of bowel obstruction.

  • Observe for the “closed eyes sign” whereby someone with a functional origin to their abdominal pain is more likely to keep their eyes closed during abdominal palpation, whereas the patient with an organic etiology is more likely to hold their eyes open. The thought is that the patient with organic disease wants to watch the doctor and avoid severe pain when able.

Pelvic Exam

  • Warranted when there are lower abdomen and/or pelvic symptoms on history or a change in menses or vaginal discharge.

Digital Rectal Examination

  • Particularly important when there are symptoms of incontinence or dyschezia in the history. Also valuable to identify a dysfunctional sphincter, paradoxical pelvic floor contraction, dyssynergic defecation, fecal impaction, or rectal cancer.

Note: Pelvic, digital, and perianal examinations are typically performed by gastroenterologists or primary care physicians before a pain consultation, and repeating this exam is not necessary.


Cultivating a trusting doctor–patient relationship is paramount. , Patients who have a good rapport with their physicians have fewer IBS-related follow-up visits. Psychiatric and functional comorbidities are common among IBS patients. An educational discussion about the unifying concept that explains many of their symptoms (central sensitization) can be relieving and therapeutic in and of itself. The treatment of IBS includes both pharmacologic and nonpharmacologic interventions, and there is no data to support any one agent or modality as first-line therapy for IBS.

Pharmacologic Agents

Of the pharmacologic interventions, there are central and peripherally acting modalities. The peripherally acting agents work at the gut level — treating the bloating, cramping, and abnormal bowel movements of IBS. Many of these agents take advantage of the deranged serotonin (5HT) levels found at the peripheral gut level in IBS. These agents include the antispasmodics (e.g., pinaverium, mebeverine, colpermin, hyoscyamine, and dicyclomine) that mechanistically are anticholinergic, smooth muscle relaxants ( Table 19.2 ). Serotonergic agents (e.g., alosetron and tegaserode) also work at the peripheral level as 5HT3 receptor antagonists and 5HT4 receptor agonists. Peripherally acting medications are not designed to treat the pain of IBS; however, they are an important complement and in some mild cases may provide sufficient symptom management.

Jan 3, 2021 | Posted by in PAIN MEDICINE | Comments Off on Irritable Bowel Syndrome
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