No antibody response in cutaneous manifestations associated with COVID‐19: An observational study of 64 cases with microbiological and clinical characterization

Background: The microbiological diagnosis of skin lesions related to COVID‐19 is not well known. Objective: Perform a microbiological diagnosis in COVID19‐related cutaneous manifestations. Methods: A cross‐sectional study was performed with 64 patients with cutaneous manifestations associated with COVID‐19 who underwent serological and nasopharyngeal reverse transcription polymerase chain reaction (RT‐PCR) for SARS‐CoV‐2. Results: Out of the 64 patients, 6 patients had positive RT‐PCR, with all of them developing SARS‐CoV‐2 IgG and 4 of them had positive IgM + IgA. Of the 58 patients with negative RT‐PCR, 8 cases had positive IgM + IgA and only one of them had IgG seroconversion. Therefore, the infection was demonstrated in 7 cases (10.9%) and was doubtful in 7 other cases (10.9%) who presented negative RT‐PCR and presence of IgA + IgM without subsequent seroconversion of IgG. Fifty patients (78.1%) had negative serological tests. The most frequent cutaneous pattern was pseudo‐chilblain (48.4%) followed by maculo‐papular pattern (26.6%), urticarial lesions (10.9%), vesicular eruptions (6.3%) and livedoid pattern (4.7%). The maculo‐papular pattern showed the highest positivity in RT‐PCR (3 cases; 17.6%) and serologies (4 cases; 23.5%). Skin lesions developed after the systemic symptoms in most patients (19 cases; 61.3%). Conclusions: Microbiological confirmation tests may not be an effective diagnostic technique for COVID‐related cutaneous manifestations or that attributed lesions are not related to COVID‐19. Confounding factors such as adverse drug reaction, serological cross‐reactions with other viruses, the low production of antibodies in asymptomatic or mild forms of COVID‐19 or its rapid disappearance, increase diagnostic uncertainty.