Colonic Eosinophilia: Clinicopathologic Study of Paired Right and Left Colon Biopsies from 276 Patients

This study evaluated differences in eosinophil (Eos) count in the right colon (RC) and left colon (LC) relative to known clinical and pathologic features.

H&E slides from 276 subjects with biopsies taken from both RC and LC were reviewed. Eos/mm2 were counted in the area with highest concentration then correlated with clinical and pathologic findings for RC and LC.

There were higher numbers of Eos/mm² in RC than in LC (mean 177 vs 122, respectively p<0.0001), and there was significant positive correlation between Eos numbers in the two locations (r=0.57, p<0.001). In RC, the mean Eos/mm² was 242 with active chronic colitis, 195 with inactive chronic colitis, 160 in microscopic colitis, 144 in quiescent IBD, and 142 with normal histology (p<0.001), and was higher in males (204 vs 164, p=0.022). In LC, mean Eos/mm² was 186 with active chronic colitis, 168 with inactive chronic colitis, 154 in microscopic colitis, 82 in quiescent IBD, and 84 with normal histology (p<0.001), and was higher in males (154 vs 107, p<0.001). In biopsies with normal histology, RC showed higher mean Eos/mm² in Asian patients (228 vs 139, p=0.019), and patients with history of UC (205 vs 136, p=0.004), but was not significantly different in patients with or without irritable bowel syndrome with diarrhea (IBS-D) or history of Crohn's disease (CD). In LC the mean Eos/mm² was higher in males (102 vs 77, p=0.036), and history of CD (117 vs 78, p=0.007), but was not significantly different in patients with or without IBS-D or history of UC. The number of Eos/mm² was greater in biopsies performed in the summer than during other seasons of the year.

The mean number of Eos/mm² in colorectal biopsies varies significantly by location, histopathologic changes, clinical diagnosis, season, gender and ethnicity. Of particular interest is the association between high Eos/mm² in RC biopsies with otherwise normal histology and clinical history of UC, and in LC biopsies with clinical history of CD. Additional larger and prospective studies that include normal healthy volunteers are needed to establish a reliable cutoff for the histopathologic diagnosis of eosinophilic colitis, taking into consideration the biopsy site within the colon and rectum, as well as patient gender and ethnicity.Presented in part at the annual American College of Gastroenterology meeting, San Antonio, TX October 2019.