Abstract
BACKGROUND: New-onset lichen planus (LP) development following COVID-19 infection/vaccination is reported. Since case series cannot be used to study exposure-outcome associations, we designed this matched case-control study to investigate whether COVID-19-related events and de novo LP are associated. METHODS: Patients with histologically confirmed LP, newly diagnosed at the National Research Center of Dermato-Venereology of Moscow (September 2020-December 2022), were considered. Sex/age/ethnicity-matched controls attending the same Center in the same period for consultations on conditions unrelated to LP were selected. Cases/controls with known LP trigger factors were excluded. COVID-19-related events were: symptomatic COVID-19 (PCR-confirmed), and COVID-19 vaccination (viral vector vaccine) occurred ≤ 1 month before the visit at the Center. The association between COVID-19-related events and LP was assessed with conditional (Mantel-Haenszel method) and unconditional (logistic regression analysis adjusted for sex, age, and smoking) analyses. Subgroup analysis, with COVID-19 infection and vaccination treated separately, and sensitivity analysis on another group of patients with suspected LP, not confirmed histologically, were also made. RESULTS: Fifty-five case-control pairs were considered. Mean age (51 years), sex (56.4% females) and ethnicity (100% whites) distributions were the same in both groups. Conditional and unconditional odds ratios resulted 7.50 (95% Confidence Interval -95CI, 1.72-32.80), 4.45 (95CI, 1.63-12.15), respectively (p < 0.05). Subgroup analysis confirmed the association between symptomatic infection and LP, while sensitivity analysis corroborated the results of the primary analysis. CONCLUSIONS: This observational study, reporting a strong significant association between COVID-19 infection/vaccination and de-novo LP, suggests that COVID-19-related events, especially infection, could act as LP trigger factors.