Microscopic Colitis: A Diagnostic Challenge in Patients with Irritable Bowel Syndrome

Background and Aims: Irritable Bowel Syndrome (IBS) is one of the most frequently diagnosed gastrointestinal disease with a prevalence of 4.1% in the general population. It is diagnosed using the Rome IV criteria. Microscopic colitis (MC), collagenous/lymphocytic colitis is a cause of chronic, watery, non-bloody diarrhea. It is a real challenge to diagnose MC in patients with IBS. The aims of the study were to determine the prevalence of MC in patients initially diagnosed with IBS, as well as to correlate fecal calprotectin levels with the endoscopic findings and microscopic inflammation in MC. Methods: This is a retrospective study conducted in a single tertiary center with over 89 IBS patients for a period of 4 years. The patients included were patients diagnosed with IBS predominant diarrhea (IBS-D) and mixed IBS (IBS-M) using the Rome IV criteria. Total colonoscopy was performed in these patients, multiple biopsies being taken and calprotectin levels were measured. Results: Out of a total of 89 IBS-D patients, 58 patients (65.2%) had no microscopic lesions, 12 patients (13.5%) had diverticular disease, 9 patients (10.1%) had non-specific chronic inflammation of the colon mucosa and 10 patients (11.2%) were diagnosed with MC. The calprotectin levels ranged from 49 μg/g to 213 μg/g. Of a total of 10 patients diagnosed with MC, 6 (60%) of them had calprotectin levels <100 μg/g and 4 (40%) had calprotectin levels >100 μg/g. The fecal calprotectin levels were higher in patients diagnosed with MC compared to those who had no microscopic lesions at the histological exam and it was also correlated with the grade of colonic microscopic inflammation. Conclusions: Microscopic colitis is less familiar to physicians and can be clinically misdiagnosed as IBS-D. An early and correct diagnosis is important for an accurate therapy.