Irritable Bowel Syndrome

Introduction

• Description: A functional syndrome of intermittent abdominal pain, constipation, and diarrhea related to hypermotility of the gut in the absence of any organic cause.

• Prevalence: 15% of the population. First described in 1818 and accounts for 50% of all visits to gastroenterologists; 2.4–3.5 million physician visits per year and an estimated 2.2 million prescriptions. Despite the prevalence of irritable bowel syndrome (IBS), only approximately 25% of those with IBS seek care and only 1% of those with IBS are referred to specialists or become chronic health care users.

• Predominant Age: Young to middle age.

• Genetics: No genetic pattern; the female-to-male ratio is 2:1. Females are more likely to have constipation-predominant IBS.

Etiology and Pathogenesis

• Causes: Colonic wall motility is altered unpredictably in patients with IBS, with evidence suggesting altered colonic wall sensitivity. Patients with IBS have altered motor reactivity to various stimuli, including meals, psychologic stress, and balloon distention of the rectosigmoid, resulting in altered transit time, which in turn results in pain, constipation, and diarrhea. Studies of patients with and without IBS revealed that there are significantly higher levels of 5-hydroxytryptamine (5-HT) in patients with IBS, supporting a possible causal role. Recent studies have considered the role of inflammation, alterations in fecal flora, and bacterial overgrowth.

• Risk Factors: None known; prior infectious gastroenteritis has been postulated as a risk factor.

Signs and Symptoms

• Intermittent abdominal pain (crampy in character, often worse before menses)

• Bloating and nausea

• Alternating constipation and diarrhea

• Tenesmus

Symptoms are generally worse 1–1.5 hours after meals, with 50% of patients experiencing pain that lasts for hours or days; pain may last for weeks in up to 20% of patients. Pain is generally worse with high-fat meals, stress, depression, or menstruation and is better after bowel movements. There are four common clinical variants: (1) IBS with constipation characterized by chronic abdominal pain and constipation; (2) IBS with diarrhea, which is usually painless; (3) mixed IBS with alternating diarrhea and constipation; and (4) unsubtyped IBS (see box).

Diagnostic Approach