Original StudyErythema Migrans and Interface Changes: More Than a Fortuitous AssociationTekin, Burak MD*; Song, Yali MD*; DiCostanzo, Damian MD†; Lee, Bonnie A. MD*Author Information *Ackerman Academy of Dermatopathology, NY; Dr. Lee is now with the Department of Dermatology, University of California, Irvine. Dr. Song is now with the Department of Dermatology, Shandong Provincial Hospital affiliated to Shandong University Jinan, China; and †Dermpath Diagnostics, Port Chester, NY. Correspondence: Burak Tekin, MD, Ackerman Academy of Dermatopathology, NY 408 8 1/2 Avenue NW E310, Rochester MN 55901 (e-mail: email@example.com). The authors declare no conflicts of interest. The findings of this study were partially presented orally at the 22nd Joint Meeting of the International Society of Dermatopathology; February 27, 2019; Arlington, VA. This study was considered exempt from review by Quorum Review IRB (QR#: 33653; date: October 23, 2018). The American Journal of Dermatopathology: October 2020 - Volume 42 - Issue 10 - p 745-750 doi: 10.1097/DAD.0000000000001631 Buy Metrics Abstract The histology of erythema (chronicum) migrans (ECM) is classically described as a nonspecific perivascular infiltrate with a variable number of plasma cells and eosinophils. However, deviations from this pattern were described, such as focal interface changes or spongiosis, potentially posing a clinicopathological challenge. In this study, cases submitted with a serologically confirmed, clinically unequivocal, or highly suspicious diagnosis of ECM/Lyme disease between January 01, 2016, and September 01, 2018, were retrieved from the electronic database system and reviewed to delineate the histopathologic features of ECM. The series consisted of 14 cases. A superficial perivascular lymphocytic infiltrate was noted in all biopsies, accompanied by a deep and/or interstitial inflammatory infiltrate in 9 cases (64%). The inflammation ranged from relatively sparse to dense and prominent. At least focal interface changes were noted in 12 biopsies (86%). Eosinophils and plasma cells were noted in 7 (50%) and 10 (71%) cases, respectively. From a histologic standpoint, ECM is a protean entity and may manifest with a variable density of perivascular and/or interstitial lymphocytic infiltrate admixed with eosinophils and/or plasma cells and accompanied by focal interface dermatitis. Within the appropriate clinical context, ECM should be considered in the differential diagnosis of focal interface and/or sparse perivascular dermatitis. Copyright © 2020 Wolters Kluwer Health, Inc. All rights reserved.