ALOX15 immunohistochemistry AIDS in the diagnosis of eosinophilic esophagitis on pauci-eosinophilic biopsies in children

Histologically, esophageal biopsies should have 15 intraepithelial eosinophils (IEEs) per high power field (HPF) to support a clinicopathologic diagnosis of eosinophilic esophagitis (EoE). Children with clinically apparent EoE may show pauci-eosinophilic biopsies due to patchy involvement. Immunostaining (Immunohistochemistry) for arachidonate-15 lipooxygenase (ALOX15) has been demonstrated to be a sensitive marker for EoE. We retrospectively assessed the expression of ALOX15 in 48 biopsies from 21 patients with established diagnosis of EoE and with tissue fragments below the threshold of 15 IEEs/HPF. Fragments were classified into pauci-eosinophilic and non-pauci-eosinophilic groups using cutoffs of 10 and 15 IEEs/HPF. Controls included patients with reflux and normal biopsies. Sixty-five (43.9%) fragments showed <10 IEEs/HPF and 83 (56.1%) showed 10 IEEs/HPF. Using a cutoff of 15 IEEs/HPF, 87 (58.7%) fragments showed <15 IEEs/HPF while 61 fragments (41.2%) had 15 IEEs/HPF. ALOX15 was positive in 53/65 (81.5%) of fragments with <10 IEEs/HPF versus 82/83 (98.8%) of fragments with 10 IEEs/HPF (P<.001). For a cutoff of 15 IEEs/HPF, 75/87 (86.2%) of pauci-eosinophilic fragments were ALOX15-positive, while 60/61(98.4%) of biopsies meeting the threshold were positive (P<.001). In 3/21 (14.3%) patients with EoE, all of the fragments (n=7) were pauci-eosinophilic and all of them were positive for ALOX15. Two of 24 patients with reflux (one with 9 and one with 14 IEEs/HPF) were also positive. Fragments from normal controls (0 IEEs/HPF) were negative. Our results support the utility of ALOX15 immunohistochemistry in supporting the diagnosis of EoE in rare situations with strong clinical suspicion where no fragments reach 15 IEEs/HPF.