Extraordinary Case ReportEarly Erythema Migrans: Do Not Count on Plasma CellsBrem, Candice E. MD; Goldberg, Lynne J. MD Author Information Section of Dermatopathology, Department of Dermatology, Boston University School of Medicine, Boston, MA. Correspondence: Candice E. Brem, MD, Section of Dermatopathology, Department of Dermatology, Boston University School of Medicine, 609 Albany Street, J-301, Boston, MA 02118 (e-mail: [email protected]). The authors declare no conflicts of interest. The American Journal of Dermatopathology: February 2022 - Volume 44 - Issue 2 - p e23-e25 doi: 10.1097/DAD.0000000000002058 Buy Metrics Abstract Three hundred thousand new cases of Lyme disease are diagnosed annually in the United States. The earliest manifestation of the disease, erythema migrans, occurs earlier than serologic conversion, and skin biopsies can be very helpful in suggesting the diagnosis. Histopathologic findings vary depending on where in the lesion the specimen is taken, but typically consist of a superficial and deep perivascular and interstitial lymphocytic infiltrate with eosinophils centrally and with histiocytes and plasma cells at the periphery. Rare cases with interstitial histiocytes and rare-to-sparse plasma cells exist. We present a 67-year-old man whose skin biopsy, taken on day 2 of his eruption, demonstrated a subtle perivascular and interstitial infiltrate of histiocytes without plasma cells. Dermatopathologists need to be aware of this pattern and consider the diagnosis of erythema migrans, despite negative initial serologic testing. Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.