Patients with Microscopic Colitis Are at Increased Risk of Inflammatory Bowel Disease

Several lines of inquiry suggest that microscopic colitis, characterized by nearly normal-appearing mucosa, shares pathogenic mechanisms with inflammatory bowel disease (IBD). For example, researchers at Massachusetts General Hospital recently demonstrated that, as in patients with IBD, the gut microbiome in patients with microscopic colitis is associated with marked dysbiosis and decreased diversity.

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Using 20 years of data from a large population-based registry, Massachusetts General Hospital's Hamed Khalili, MD, MPH, gastroenterologist, and Kristin E. Burke, MD, MPH, inflammatory bowel disease physician in the Crohn's and Colitis Center, and Jonas F. Ludvigsson, MD, PhD, of the Karolinska Institutet, and colleagues conducted the first systematic study to examine this putative relationship. In Gastroenterology, they report a significant increase in the risk of IBD among patients with microscopic colitis.

Study Subjects and Methods

The researchers studied 13,957 Swedish adults with microscopic colitis who were diagnosed after January 1, 1990, and had gastrointestinal-related biopsies available through the ESPRESSO study (Epidemiology Strengthened by histoPathology Reports in Sweden).

Each patient with microscopic colitis was matched with as many as five controls according to age, sex, calendar year and county of residence at the date of diagnosis. The 66,820 controls were derived from the Total Population Register, which maintains data on all Swedish residents.

The researchers used the Swedish Patient Register to determine incident cases of IBD, which they defined as at least two inpatient or outpatient encounters with a primary or secondary diagnosis of Crohn's disease (CD) or ulcerative colitis (UC).

IBD Risk

During the follow-up period, 108 patients with microscopic colitis and 42 controls developed CD. For UC, the respective figures were 323 and 94.

For those patients, the average time to diagnosis of either CD or UC was about three years after the diagnosis of microscopic colitis.

Multivariable Analyses

When adjusted for age, sex, calendar year, county, celiac disease and type 2 diabetes, the hazard ratios were:

• CD, UC and IBD-unclassified considered together—16.8 (95% CI, 13.9–20.3)
• CD—12.6 (95% CI, 8.8–18.1)
• UC—17.3 (95% CI, 13.7–21.8)

The 20-year absolute excess risk was 1.1 percentage points for CD and 3.6 percentage points for UC.

Subgroup Analyses

The associations between microscopic colitis and IBD were similar regardless of:

• Histologic subtype (collagenous or lymphocytic colitis)
• Choice of medication used for initial treatment
• Age at diagnosis of microscopic colitis
• Duration of follow-up
• Sex
• Educational level

An Attenuated Form of IBD?

In another study published in Digestive Diseases and Sciences, patients who had microscopic colitis, then developed classical IBD, showed higher expression of certain cytokines and transcription factors than patients whose microscopic colitis did not progress. It's possible that microscopic colitis is an attenuated form of IBD—mucosal inflammation largely remains in check but progresses if compensatory mechanisms fail.

Microscopic colitis principally affects older adults, so it may be a risk factor only for older-onset IBD. Whatever the exact relationship proves to be, gastroenterologists who remain cognizant of it will be able to make a timely diagnosis if the nature of symptoms changes in patients with microscopic colitis.

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