2. Skin manifestations associated with thrombovascular events and vascular pathologies
COVID-19 exanthems have also been reported with petechiae and low platelet count resembling dengue (30). In two patients, unilateral lesions on the thigh resembling livedo reticularis or erythema ab igne have been described with microthromboses discussed as possible etiology (Figure 3A) (31).
Chilblain-like skin lesions have been frequently reported to be associated with COVID-19 (22,32,33,34) (Figure 3B(32)). They appear in up to 19% of patients, typically in mildly affected ones, and late in the evolution of the disease (22,34). Vesicles, pustules and erosions on these violaceous plaques may occur (34). In Spain they were observed in 19% of 375 cases (22).
Seven patients had cutaneous acro-ischemia including finger and toe cyanosis, skin bulla and dry gangrene associated with COVID-19 infection-induced hypercoagulation including definitive DIC in four patients. Five of these patients finally died (Figure 3C)(35). A catastrophic microvascular injury syndrome mediated by activation of complement pathways and an associated procoagulant state were described in severe COVID-19 with purpuric skin rash in 3/5 patients (36).
In conclusion, the prevalence of cutaneous manifestations in COVID-19 patients has been reported between 0.2%, 4.9% and 20.9% (4,21,27). Most skin manifestations resemble cutaneous involvement commonly occurring during viral infections, i.e. erythematous rash and acute urticaria. Drug exanthems have to be considered as differential diagnosis (15). Vesicular varicella-like exanthems may be more specific for COVID-19. Flexural distribution, and petechia as well as erythema ab igne-like lesions have been described. Violaceous, infiltrated painful plaques resembling chilblains have been frequently reported and discussed as typical manifestations. Necrotic lesions occurred in older and in severely ill patients with increased mortality (22). Cutaneous acro-ischemic microthromboses and small blood vessel occlusion have to be further explored for their causality and specificity for COVID-19 manifestations.