SARS‐CoV‐2 endothelial infection causes COVID‐19 chilblains: histopathological, immunohistochemical and ultraestructural study of 7 paediatric cases

Colmenero, I.; Santonja, C.; Alonso‐Riaño, M.; Noguera‐Morel, L.; Hernández‐Martín, A.; Andina, D.; Wiesner, T.; Rodríguez‐Peralto, J.L.; Requena, L.; Torrelo, A.

BACKGROUND: Chilblains ("COVID toes") are being seen with increasing frequency in children and young adults during the COVID‐19 pandemic. Detailed histopathological descriptions of COVID‐19 chilblains have not been reported, and causality of SARS‐CoV‐2 has not been established yet. OBJECTIVE: To describe histopathological features of Covid‐19 chilblains and explore the presence of SARS‐CoV‐2 in the tissue. METHODS: We examined skin biopsies from 7 paediatric patients presenting with chilblains during the COVID‐19 pandemic. Immunohistochemistry for SARS‐CoV‐2 was performed in all cases and electron microscopy in one. RESULTS: Histopathology showed variable degrees of lymphocytic vasculitis ranging from endothelial swelling and endothelialitis to fibrinoid necrosis and thrombosis. Purpura, superficial and deep perivascular lymphocytic inflammation with perieccrine accentuation, oedema, and mild vacuolar interface damage were also seen. SARS‐CoV‐2 immunohistochemistry was positive in endothelial cells and epithelial cells of eccrine glands. Coronavirus particles were found in the cytoplasm of endothelial cells on electron microscopy. CONCLUSIONS: Although the clinical and histopathological features were similar to other forms of chilblains, the presence of viral particles in the endothelium and the histological evidence of vascular damage, support a causal relation of the lesions with SARS‐CoV‐2. Endothelial damage induced by the virus could be the key mechanism in the pathogenesis of COVID‐19 chilblains and perhaps also in a group of patients severely affected by COVID‐19 presenting with features of microangiopathic damage.