Fast Five Quiz: Do You Know Key Differences Between Irritable Bowel Syndrome and Inflammatory Bowel Disease?

Jamie Shalkow, MD; Daniel Margain, MD


July 12, 2018

Approximately 50% of people with IBS report symptoms beginning before age 35 years. The development of symptoms in people older than 40 years does not exclude IBS but should prompt a closer search for an underlying organic etiology.

The age distribution of newly diagnosed IBD cases is bell-shaped; the peak incidence occurs early in the second decade of life, with the vast majority of new diagnoses made in people aged 15 to 40 years. A second, smaller peak in incidence occurs in those aged 55 to 65 years and is increasing. Approximately 10% of IBD patients are younger than 18 years.

Persons with IBD have a genetic susceptibility for the disease. First-degree relatives have a 5- to 20-fold increased risk of developing IBD compared with persons from unaffected families. The child of a parent with IBD has a 5% risk of developing IBD. The causes of IBS remain poorly defined but are being avidly researched. Some studies have identified mutations in the SCN5A gene. Several genetic syndromes have been associated with IBD, including Turner syndrome, Hermansky-Pudlak syndrome, and glycogen-storage disease type 1b.

The male-to-female ratio is approximately 1:1 for CD, with females having a slightly greater incidence. Male sex has been associated with a higher incidence rate of UC compared with females (12.8 vs 8.8 case per 100,000 person-years). In Western countries, women are two to three times more likely than men to develop IBS.

Current smoking increases the risk for CD. However, current smoking protects against UC, whereas former smoking increases the risk for UC. Risk factors for developing postinfectious IBS include longer duration of illness, the type of pathogen involved, smoking, female gender, an absence of vomiting during the infectious illness, and young age. Smoking has not shown to be protective in IBS.

For more on the etiology and epidemiology of IBD, read here.


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