RESUMEN
[...]a combined study of prospective testing in Eastern Spain and retrospective literature review of acral cases in both adults and children found only 13 out of 88 (14.8%) tested cases were positive for COV-ID-19 .5 The PCR/serology testing of 38 children (median age 13.5 years) with new onset pseudo-chilblains at a tertiary care hospital in Italy found all patients negative for RT-PCR and IgM, IgG, IgA antibodies.7 A potential confounding variable is lifestyle changes from staying indoors during a lockdown state, implemented by many countries in response to the COVID-19 pandemic. An in-depth study by Neri and colleagues8 of 8 adolescents with chilblains-like lesions revealed that they had increased risk factors for primary chilblains: body mass index (BMI) <50th percentile, increased cold exposure with barefoot or thin socks contacting with cold floors, and prolonged postural habits impeding robust peripheral circulation. Initial viral testing is biased towards patients with URI symptoms, the timing of retrospective testing is variable, and much is still unknown about COVID-19 antibodies-including the percentage of who acquires these antibodies and the duration of positive serology.9,10 Reports of pseudo-chilblains associated with COVID-19 have presented consistent histological findings of superficial, deep, and perivascular lymphocytic infiltrate regardless of positive or negative COVID-19 testing in the patient,6'11'12 suggesting an inflammatory-based etiology that differs from the post-infectious perniosis histology commonly involving cold agglutinins and cryoglobulins.13 Interestingly, even in some pediatric cases with negative SARS-CoV-2 PCR, biopsies still demonstrated SARS-CoV-2 positive im-munohisto chemistry in endothelial cells.12,14 The positive immunohis-tochemistry was confirmed on electron microscopy with coronavirus particles present in endothelial cell cytoplasm,12 suggesting that the virus may still play a role in inducing lymphocytic vasculitis in pseudo-chilblains, despite negative PCR or serum serology. The Pediatric Dermatology Research Alliance COVID-19 Response Task Force (PDCRTF) has developed an open registry for cases to study and better understand this phenomenon.18 Other vascular related skin manifestations such as livedo-reticularis and purpuric or petechial eruptions have been reported in adults and were felt to be a thrombotic phenomenon related to viral infection, but a literature search has not revealed such cases among children up to date of this publication except for one case of petechiae presenting in relation to other morbilliform and annular lesions discussed later.19 Nonspecific viral exanthems A series of cases highlight a varicella-like exanthem associated with COVID-19 among adult patients, particularly in Italy, who developed a monomorphic papulovesicular rash of the trunk that progressed to crusting over a few days with histology consistent with viral infection.20 Among children, Genovese and colleagues21 detailed a similar varicella-like papulovesicular exanthem, distributed symmetrically along the bilateral trunk.