Post-COVID-19 and Post-COVID-19 Vaccine Arthritis, Polymyalgia Rheumatica and Horton's Arteritis: A Single-Center Assessment of Clinical, Serological, Genetic, and Ultrasonographic Biomarkers.

The potential role of the COVID-19 vaccine and infection to induce autoimmunity is currently underestimated despite the literature emphasizing arthralgia as a common adverse event. We aimed to study the impact of rheumatological complications post-COVID-19 (PC) and post-COVID-19 vaccine (PCV), comparing undifferentiated arthritis (UA) to Polymyalgia Rheumatica, Horton's Arteritis (PMR-HA) and isolated arthritis to UA with "connective-like" accompanying symptoms. We retrospectively included 109 patients with at least 6 months of follow-up, analyzing serum biomarkers, joint ultrasound (US), lung HRCT, DLCO, and HLA haplotypes. There were 87 UA patients showing increased gastrointestinal and lung involvement ( = 0.021 and = 0.012), higher anti-spike protein IgG levels ( = 0.003), and anti-SARS-CoV-2 IgG positivity ( = 0.003). Among them, 66 cases progressed to ACR-EULAR 2010 early arthritis after 3 months, whereas PMR-HA patients were more commonly PCV (81.8%, = 0.008), demonstrating higher CRP ( = 0.007) and ESR ( = 0.006) levels, a lower rate of ANA positivity ( = 0.005), and a higher remission rate after six months ( = 0.050). In UA patients, the prevalent HLA was DRB1*11 and C*07 (36.8% and 42.1%). Serum calprotectin, interleukin-6, and C*07 ( = 0.021, 0.041, 0.018) seemed more specific for isolated UA. Conversely, "connective-like" arthritis showed poorer DLCO ( = 0.041) and more frequent US synovitis ( = 0.041). In conclusion, UA is a frequent common PC and PCV complication and may persist over time when compared to PMR-HA.