Abstract

A 50-year-old woman was admitted to a Florida hospital with thrombocytopenia, elevated liver enzymes, cervical lymphadenopathy, fever, and a diffuse rash of 3-day duration. The patient denied travel outside the Southeastern United States but worked in an animal shelter. Initially, an eschar developed on the thigh followed by a generalized papulovesicular eruption. The clinical impression was rickettsialpox. A punch biopsy from a papulovesicle demonstrated edema, lymphocytic vasculitis, and hemorrhage. A second biopsy from the eschar demonstrated ulceration, necrosis, and granulomatous vasculitis. Deeper sections from the eschar revealed retained tick mouth parts, excluding the possibility of R. akari infection. Each biopsy and whole blood were submitted to the Centers for Disease Control to identify a causative Rickettsia species. Immunohistochemical stain for Spotted fever group Risckettsia was positive. Real-time PCR detected the presence of R. parkeri DNA in the biopsy from the papulovesicle. PCR was negative in whole blood and the eschar biopsy, given that doxycycline administration preceded the collection of these specimens. Indirect immunofluorescence assay of sera collected 3-days after symptom onset (acute phase) and 6-weeks later (convalescent phase) confirmed IgG antibodies with cross-reactivity to R. risckettsii (1:128; 1:2048), R. akari (1:128; 1:1024), and R. parkeri (1:128; 1:1024). A diagnosis of R. parkeri rickettsiosis was confirmed given the presence of eschar with papulovesicular eruption, geography, retained tick mouth parts, and PCR results. A 10-day course of doxycycline produced rapid resolution. R. parkeri is transmitted by the Gulf Coast tick (Amblyomma maculatum) and causes a febrile illness that can simulate rickettsialpox due to R. akari. This abstract will highlight the histopathologic features, diagnostic methods with potential pitfalls, and clinical correlations that permit dermatopathologists to classify rickettsioses.

Financial Disclosure:
No current or relevant financial relationships exist.