Are chilblains a skin expression of COVID-19 microangiopathy?

Clinical Patterns and Morphology of COVID-19 Dermatology

Coronavirus disease 2019 (COVID-19), an emergent disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has rapidly spread throughout the globe since its discovery in December 2019. Although first appreciated to cause pneumonia, numerous organ systems are now known to be involved. The objective of this article is to review the broad spectrum of cutaneous manifestations reported in association with SARS-CoV-2 infection. The most commonly reported cutaneous manifestations associated with COVID-19 infection include pernio (chilblain)-like acral lesions, morbilliform (exanthematous) rash, urticaria, vesicular (varicella-like) eruptions, and vaso-occlusive lesions (livedo racemosa, retiform purpura). It is important to consider SARS-CoV-2 infection in the differential diagnosis of a patient presenting with these lesions in the appropriate clinical context, as cutaneous manifestations may be present in otherwise asymptomatic individuals, or present before developing other symptoms of infection. With increased access to diagnostic testing, we are beginning to understand the utility and limitations of currently available assays.

COVID toes: where do we stand with the current evidence?

BACKGROUND

Numerous of cases of chilblains have been observed, mainly in young subjects with no or mild symptoms compatible with COVID-19. The pathophysiology of these lesions is still widely debated and an association with SARS-CoV-2 infection remains unconfirmed.

OBJECTIVES

This paper focus on the unresolved issues about these COVID toes and in particular whether or not they are associated with COVID-19.

ARGUMENTS

The temporal link between the outbreak of chilblains and the COVID-19 pandemic is a first suggests a link between the two events. Positive anti-SARS-CoV/SARS-CoV-2 immunostaining on skin biopsy of chilblains seem to confirm the presence of the virus in the lesions, but lack specificity and must be interpreted with caution. Conversely, RT-PCR and anti-SARS-CoV-2 serology were negative in the majority of patients with chilblains. Therefore, SARS-CoV-2 infection can be excluded, with relative certainty, even after accounting for possible lower immunization in mild/asymptomatic patients and for some differences in sensitivity/specificity between the tests used. Some authors hypothesize that chilblains could be the cutaneous expression of a strong type I interferon (IFN-I) response. High production of IFN-I is suggested to be associated with early viral control and may suppress antibody response. However, the absence of other cutaneous or extracutaneous symptoms as observed in other interferonopathies raises unanswered questions. To date, a direct link between chilblains and COVID-19 still seems impossible to confirm. A more indirect association due to lifestyle changes induced by lockdown is a possible explanation. Improvement of chilblains when protective measures were adopted and after lifting of lockdown, support this hypothesis.

CONCLUSION

Conflicting current evidence highlights the need for systematic and repeated testing of larger numbers of patients and the need for valid follow-up data that take into consideration epidemic curves and evolution of lockdown measures.