COVID-19-related dermatosis in November 2019: could this case be Italy's patient zero?

Abstract

Dear Editor, Milan, the largest city in northern Italy, was one of the first European metropolitan areas to be affected by the coronavirus disease 2019 (COVID‐19) pandemic. We analysed skin biopsies of patients from Milan with dermatoses and positive polymerase chain reaction (PCR) swabs for SARS‐CoV‐2 at different stages of infection.1, 2 The results were compared with skin biopsies of 20 patients with dermatoses who had not been diagnosed with COVID‐19, but were at high risk of infection. They were considered high risk because they either presented with mild COVID‐19 symptoms or had been in close contact with individuals who were positive for SARS‐CoV‐2. Histopathological features and patterns showed no differences between these two groups. Furthermore, 70% of the skin samples from the ‘high‐risk’ group were immunohistochemically positive for SARS‐CoV‐2 nucleocapsid antigens.2 In November 2019, a 25‐year‐old woman presented with urticarial plaque‐like dermatosis on the arms (Figure 1a). The only systemic symptom she complained about was a mild sore throat. A punch biopsy showed a dense perivascular and periglandular infiltration. We suspected ‘lupus erythematosus tumidus’. A PCR swab was not performed. (a) Large urticarial erythematous plaques on the arms. (b) Minichilblain pattern demonstrating both superficial and deep perivascular dermatitis. (c) Massive lymphocytic infiltration surrounding deep eccrine glands. Immunohistochemical investigations for SARS‐CoV‐2 nucleocapsid antigens showed a cuticular staining of the glomerular part of the eccrine glands (inset). (d) In the context of the tubuloglandular structures, RNA fluorescence in situ hybridization (FISH) shows clear, strong, red bar‐like signals. Further sections of the same samples were pretreated with RNase to avoid false‐positivity. The RNA‐FISH result was negative (inset). In July 2020, we realized that the histopathological features of the biopsy matched the minichilblain pattern described in our previously published paper on COVID‐19‐related dermatoses (Figure 1b, c).2 Hence, we decided to study this biopsy again. We performed immunohistochemical investigations for SARS‐CoV‐2 nucleocapsid antigens on paraffin sections. We employed nine dermatoses biopsies and six cases of basal cell carcinoma (year 2018) as negative controls. In control cases, no immunohistochemical staining was observed. As positive control cases, we used skin biopsies from three patients who were positive for SARS‐CoV‐2 who presented skin lesions during hospitalization in the intensive care unit. In all positive control cases, immunohistochemistry stained the cuticular region of the eccrine glands. We also performed RNA fluorescence in situ hybridization (FISH) analysis using the HuluFISH technique (Pixel Biotech, Heidelberg, Germany) that enzymatically labels oligonucleotide probes (oligos), enabling SARS‐CoV‐2 mRNA detection at the single‐molecule level. The SARS‐CoV‐2 probe kit consists of 96 oligos detecting the spike glycoprotein mRNA of SARS‐CoV‐2 and a portion of the viral open reading frame 1 mRNA. Normally, a minimum 200‐bp target sequence is sufficient for a custom FISH probe design. SARS‐CoV‐2 is a positive‐sense RNA virus with a size of 29 903 bp, which is more than enough to design the optimal FISH probe. Specifically, we searched for the spike glycoprotein, which is roughly 3800 bp – an ideal size for our probe design.3 We also searched for viral RNA on the same formalin‐fixed paraffin‐embedded sections with reverse‐transcriptase (RT)‐PCR technology. Immunohistochemical investigations for SARS‐CoV‐2 nucleocapsid antigens in our patient showed a cuticular staining of the glomerular part of the eccrine glands (Figure 1c, inset). In the context of the tubuloglandular structures, RNA‐FISH shows clear, strong, red bar‐like signals (Figure 1d). The sample was pretreated with RNase to avoid false‐positivity (Figure 1d, inset). We were not able to detect viral RNA with RT‐PCR technology because the viral load was probably too low or degraded by RNA enzymes released after exogenous or cellular destruction.3 By April 2020, the patient had recovered from the dermatosis. In June, the patient’s IgG SARS‐CoV‐2 serological test was positive. The present case is part of an ongoing study, where we observed the immunohistochemical positivity for nucleocapsid antigens and mRNA‐FISH in eccrine glands of seven patients with dermatosis as the only COVID‐19 clinical symptom. While the immunohistochemical positivity of spike protein antigens in eccrine glands and acrosyringia has already been demonstrated in patients with COVID‐19,4 few studies have used the RNA‐FISH technique on skin paraffin sections, but they have obtained negative or discordant results.5 To date, no study of skin lesions from patients without systemic disease has ever shown the presence of SARS‐CoV‐2 in paraffin samples with a double technique and with positive serology for IgG in the blood. No article has ever