Histopathologic Finding of Perieschar Lesions in Tsutsugamushi Disease Shows Lymphocytic Vasculitis Mimicking Angiocentric Lymphoma

Background Tsutsugamushi disease is an acute, febrile, infectious disease caused by Orientia tsutsugamushi. Several studies investigating the histopathologic findings of eschars in tsutsugamushi disease reported leukocytoclastic vasculitis and neutrophil infiltration as the major findings. However, these findings may result from secondary changes following tissue necrosis. The histopathologic findings of perieschar lesions may be important to understand the primary changes associated with tsutsugamushi disease. Objective To investigate characteristic histopathologic features of perieschar lesions and suppose the mechanism of vascular pathophysiological changes associated with tsutsugamushi disease. Methods We analyzed histopathological slides of perieschar lesions in 12 patients diagnosed with tsutsugamushi disease. Results In the epidermis, exocytosis of mononuclear cells (75.0%) and basal vacuolar changes (66.7%) were frequent. In the dermis, perivascular, interstitial, and perineural mononuclear cell infiltration (100.0%, 83.3%, and 83.3%, respectively), as well as thrombosis (83.3%), atypical lymphocyte infiltration (91.7%), and mitotic figures (83.3%) were commonly seen. Lymphocytic vasculitis and mononuclear cell infiltration around eccrine glands were found in all cases, but eosinophil infiltration was only found in one patient (8.3%). However, the characteristic findings of eschar lesions, such as leukocytoclastic vasculitis and neutrophil infiltration, were not found in perieschar lesions. Conclusion The major histopathologic findings in the perieschar lesions of tsutsugamushi disease were lymphocytic vasculitis and atypical lymphocytic infiltration, mimicking lymphoma. Therefore, we suggest that this lesion should be added to the list of pseudolymphomas. To observe these characteristic histopathologic features, we also recommend that skin biopsies should be performed on perieschar lesions, not eschar lesions.