Investigating the Histopathological Findings and Immunolocalization of Rickettsialpox Infection in Skin Biopsies: A Case Series and Review of the Literature.

BACKGROUND: Recognition of rickettsialpox infection on skin biopsy can be challenging. The histopathology is nonspecific and inconsistently described. We assess classic histopathologic features in confirmed cases and review the literature.

METHODS: We searched for cases of "rickettsialpox" diagnosed between 2006-2018 with positive immunostaining for Spotted Fever Group Rickettsia species. Original slides were evaluated for vacuolar alterations, granulomatous inflammation, vasculitis, necrosis, fibrin thrombi, microvesiculation, papillary dermal edema and extravasated red blood cells. All biopsies were stained with CD3, CD20, CD68 and myeloperoxidase.

RESULTS: Six biopsies were compiled, 3 of which were sampled from vesiculopapules, 1 from a maculopapule, and 2 from eschars. Vacuolar alterations and vasculitis were present in all biopsies (6/6; 100%). Granulomatous inflammation was present in 5 biopsies (5/6; 83.3%). Fibrin thrombi and red blood cells were seen in 3/6 (50%) of biopsies. The eschars showed necrosis of the epidermis and superficial dermis (2/6, 33.3%). Only 1 biopsy showed intraepidermal vesiculation and papillary dermal edema (1/6; 16.7%). All six biopsies showed perivascular infiltration with CD3+ T-cells, and low amounts of CD20+ B-cells and neutrophils. Five of the six biopsies (83.3%) showed significant levels of CD68+ histiocytes.

CONCLUSION: The histopathology of rickettsialpox infection is septic lymphocytic and granulomatous vasculitis. This article is protected by copyright. All rights reserved.