Development of sacral/buttock retiform purpura as an ominous presenting sign of COVID-19 and clinical and histopathologic evolution during severe disease course.

Retiform purpura has been described as a relatively frequent cutaneous finding in patients with coronavirus disease 2019 (COVID-19). The etiology is hypothesized to be related to thrombotic vasculopathy based on lesional biopsy specimen findings, but the pathogenesis of the vasculopathy is not completely understood. Here, we present a case of a retiform purpuric patch on the sacrum/buttocks in a hospitalized patient prior to subsequent diagnosis of COVID-19 and an eventual fatal disease course. Two lesional biopsy specimens at different time points in the disease course revealed thrombotic vasculopathy, despite therapeutic anticoagulation. Detailed histopathologic evaluation using immunohistochemical markers suggest the etiology of the vasculopathy involves both persistent complement activation and platelet aggregation, which possibly promote ongoing thrombus formation. This case highlights that sacral/buttock retiform purpuric patches may be a presenting sign of infection with SARS-CoV-2 virus and may represent an ominous sign supporting a future severe disease course. In addition, biopsy specimen findings at separate time points demonstrate that cutaneous vasculopathy may persist despite adequate systemic anticoagulation, possibly due to the combination of persistent complement and platelet activation. Finally, occlusive thrombi in sacral/buttock retiform purpuric patches may contribute to future ulceration and significant cutaneous morbidity in patients who survive COVID-19.