Irritable Bowel Syndrome (IBS): Diagnosis and Treatment

What Is Irritable Bowel Syndrome?

Irritable bowel syndrome (IBS) is a chronic functional gastrointestinal disorder characterized by recurrent abdominal pain associated with changes in bowel habit — diarrhea, constipation, or both alternately. There is no identifiable structural lesion in the digestive tract.

IBS affects between 10% and 15% of the world population and is more prevalent in women, with a 2:1 ratio. It is the most frequent reason for gastroenterology referral, accounting for up to 40% of consultations in the specialty.

Although it does not pose a risk to life, IBS significantly impacts quality of life. Patients with IBS show high rates of work absenteeism and social limitations comparable to organic diseases such as Crohn's disease.

Pathophysiology

IBS pathophysiology is multifactorial and involves complex interaction between central and peripheral factors. The current model recognizes IBS as a disorder of gut-brain interaction, replacing the old designation of "functional disorder."

Visceral hypersensitivity is one of the central mechanisms. Patients with IBS have reduced pain thresholds to rectal and colonic distention — distention volumes that would be imperceptible in healthy individuals generate significant pain in IBS. This hypersensitivity involves peripheral sensitization of visceral afferents and central amplification of pain processing.

Dysmotility and Microbiota

Changes in gastrointestinal motility are consistent with the disease subtypes: accelerated transit in IBS-D (diarrhea) and slow transit in IBS-C (constipation). These motor changes are mediated by dysfunction in the enteric nervous system and in intestinal serotonin levels.

Intestinal dysbiosis — alterations in the composition and diversity of the microbiota — has a recognized role in IBS. Patients with IBS show reduction of butyrate-producing bacteria and increase of pro-inflammatory bacteria. Up to 36% of IBS cases begin after acute infectious gastroenteritis (post-infectious IBS).

Symptoms

The cardinal symptom of IBS is recurrent abdominal pain associated with changes in bowel habit. The pain typically improves after defecation and worsens with emotional stress or certain foods. IBS is classified into subtypes according to the predominant pattern.

Diagnosis

The diagnosis of IBS is clinical, based on the Rome IV criteria. The positive diagnostic approach — identifying IBS by its clinical criteria — is preferred over the exclusion strategy. Complementary tests are indicated only when there are alarm signs.

Extensive exclusion diagnosis (multiple tests to rule out all possibilities) is discouraged because it increases costs, delays treatment, and can reinforce patient anxiety. Basic tests such as complete blood count, CRP, and celiac serology are recommended, especially in IBS-D.

Inflammatory Bowel Disease: Excluding the Main Organic Cause

Inflammatory Bowel Disease (IBD) — comprising Crohn's disease and ulcerative colitis — is the most relevant differential diagnosis for IBS. Both present with abdominal pain and altered bowel habit, but IBD shows alarm signs absent in IBS: rectal bleeding, persistent fever, involuntary weight loss, and elevated inflammatory markers such as fecal calprotectin, CRP, and ESR. Fecal calprotectin > 50 µg/g has sensitivity greater than 80% for active intestinal inflammation.

Physicians should request fecal calprotectin as initial screening before colonoscopy in patients with symptoms suspicious for IBS. Normal calprotectin values in a patient with typical IBS symptoms reasonably rule out the need for immediate colonoscopy. When red flags are present — regardless of age — colonoscopy is mandatory to exclude IBD and colorectal cancer.

Celiac Disease and Lactose Intolerance: Causes Treatable with Diet

Celiac disease affects about 1% of the population and frequently manifests as malabsorption syndrome with diarrhea, abdominal distention, and iron-deficiency anemia — a picture that overlaps with IBS. Clear worsening with gluten ingestion and positive anti-transglutaminase IgA antibodies (anti-tTG IgA) point toward the diagnosis. Duodenal biopsy by upper endoscopy confirms villous atrophy and is considered the gold standard.

Lactose intolerance is even more prevalent and causes symptoms identical to diarrhea-predominant IBS: distention, flatulence, diarrhea, and cramps after dairy. The hydrogen breath test with lactose confirms the diagnosis with good accuracy. Therapeutic exclusion of lactose for 2-4 weeks is a practical alternative. Unlike IBS, lactose intolerance has a direct and consistent relationship with dairy consumption.

SIBO and Colorectal Cancer: Conditions That Cannot Be Missed

Small intestinal bacterial overgrowth (SIBO) produces symptoms that mimic IBS: intense abdominal distention, excessive flatulence, belching, and diarrhea after fermentable carbohydrates. SIBO prevalence in patients diagnosed with IBS varies from 30 to 80% across studies, suggesting that some "IBS" cases are, in fact, undiagnosed SIBO. The hydrogen breath test with lactulose or glucose is the noninvasive method of choice.

Colorectal cancer requires mandatory exclusion in any patient with a recent change in bowel habit, especially after age 50 or with positive family history. Rectal bleeding, even in small amounts, involuntary weight loss, and anemia are alarm signs that make colonoscopy indispensable. IBS should never be diagnosed without carefully evaluating these red flags, since delayed diagnosis of colorectal cancer directly impacts prognosis.

Treatment

IBS treatment is multimodal and individualized, combining dietary guidance, pharmacotherapy, and psychological approaches. A quality physician-patient relationship is the first therapeutic pillar — validating symptoms and educating about the benign nature of the condition significantly reduces anxiety.

Acupuncture as Treatment

Acupuncture has been investigated as a complementary therapy for IBS, with growing — though heterogeneous — evidence. Proposed mechanisms — still under investigation — include possible modulation of the gut-brain axis, reduction of visceral hypersensitivity, regulation of gastrointestinal motility, and modulation of the inflammatory response of the mucosa.

Preliminary functional neuroimaging studies suggest that acupuncture may modulate activity in brain regions involved in visceral processing, including the anterior cingulate cortex, insula, and prefrontal cortex. These findings are exploratory and do not constitute a confirmed mechanism.

Randomized clinical trials suggest that acupuncture may help relieve abdominal pain and distention and improve quality of life in selected patients with IBS, as a complementary — not substitutive — approach to standard treatment. A typical protocol involves 8-12 weekly sessions, with periodic response assessments.

Prognosis

IBS is a chronic condition with a fluctuating course. Most patients experience periods of exacerbation and remission throughout life. There is no progression to severe organic diseases — IBS does not evolve into colorectal cancer or inflammatory bowel disease.

With adequate treatment, most patients achieve satisfactory symptom control. The multimodal approach — combining diet, pharmacotherapy, and stress management — offers the best long-term results. About 30% of patients achieve sustained remission after successful treatment.

Factors associated with better prognosis include early diagnosis, a good physician-patient relationship, adherence to dietary guidance, and adequate management of psychiatric comorbidities such as anxiety and depression, present in up to 60% of patients with IBS.

Myths and Facts

When to Seek Help

IBS warrants medical evaluation when symptoms impact quality of life, work, or social activities. Some situations require more urgent evaluation to exclude organic diseases.