Chapter 33 Irritable Bowel Syndrome
INTRODUCTION
Description: A syndrome of intermittent abdominal pain, constipation, and diarrhea related to hypermotility of the gut.
Prevalence: First described in 1818 and accounts for 50% of all visits to gastroenterologists; 2.4 to 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.
ETIOLOGY AND PATHOGENESIS
Causes: Colonic wall motility is altered in these patients, with evidence suggesting altered colonic wall sensitivity. Patients with IBS have altered motor reactivity to various stimuli, including meals, psychological 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 have shown that there are significantly higher levels of 5-hydroxytryptamine (5-HT) in those patients with IBS, supporting a possible causal role.
