What is the incidence of celiac disease in patients with microscopic colitis? Why are these two diseases related?

Introduction
Although there are studies in the literature showing that celiac disease (CD) is more common in patients with microscopic colitis (MC), there are publications to the contrary. The pathophysiologies of both diseases are different from each other.

Aim
To investigate the frequency of CD in MC patients, the different features of these 2 diseases, and the relationship between them.

Material and methods
In our prospective and cross-sectional analytical study, the presence of CD was investigated in 90 patients diagnosed with MC by colonoscopy and biopsy due to chronic diarrhoea between September 2011 and December 2021.

Results
We detected MC in 102 (9.3%) of 1096 patients investigated for chronic diarrhoea. We detected CD in 1 (1.1%) of 90 patients with MC who participated in the study. Only 10% of the patients were positive for AGA IgA, 3.3% for EMA IgA, and 2.2% for Anti-TG2 IgA. There was no difference in autoantibody titre in treatment-responsive and treatment-resistant MC patients. HLA DQ2 was positive in 32.2% (n = 29) of the MC patients, and HLA DQ8 was found in 5.5% (n = 5). Intraepithelial lymphocyte increase was remarkable in the duodenal biopsies of MC patients who did not respond to treatment (40% vs. 11.4%; p = 0.007).

Conclusions
We did not reach the conclusion that CD is more common in MC patients. An increase in IEL may also occur in the small intestine in patients with MC who do not respond to treatment.