Viral arthritis accounts for approximately 1% of acute arthritis cases and may be caused by several viruses, particularly parvovirus B19 (B19V). Diagnosis relies on clinical presentation, B19V immunoglobulin M (IgM) and/or immunoglobulin G (IgG) seropositivity, and the exclusion of other infectious and non-infectious etiologies. Following a European outbreak of B19V between March and May 2024, we conducted a multicenter retrospective study. The primary outcomes were the clinical and laboratory manifestations of B19V-associated arthritis; secondary outcomes included progression to chronic inflammatory disease and the need for escalation to disease-modifying antirheumatic drugs (DMARDs). A total of 28 patients (25 women and 3 men) were included, with a mean age of 44±11.4 years; 16 patients (57.1%) reported epidemiological risk factors. Acute, additive, symmetrical inflammatory polyarthralgia was the predominant clinical feature (26 patients, 92.9%), while axial inflammatory pain was reported by four patients (14.3%). Laboratory evaluation revealed positivity for antinuclear antibody (ANA) in 32.1%, rheumatoid factor (RF) in 19.7%, and HLA-B27 in 7.1% of patients. Anti–double-stranded DNA (dsDNA) and anti–cyclic citrullinated peptide antibodies (ACPA) were negative in all cases. Complement consumption was observed in a minority of patients, with low C3 levels in four (14.3%) and low C4 levels in three patients (10.7%). Regarding treatment, 39.3% of patients received nonsteroidal anti-inflammatory drugs (NSAIDs), while 60.7% were treated with systemic corticosteroids (prednisolone 10–40 mg/day); one patient required intravenous methylprednisolone (125 mg). Clinical remission was achieved in 24 patients (85.7%) after a mean duration of 34±47.0 days. However, four patients experienced relapse during corticosteroid tapering, suggesting potential progression to a chronic inflammatory condition. Among these, one patient achieved adequate symptom control with intermittent courses of NSAID alone, whereas the remaining three required initiation of DMARD therapy. This study provides one of the most comprehensive characterizations of B19V–associated arthritis in immunocompetent adults. Our findings emphasizes B19V infection as a significant viral mimic of early inflammatory rheumatic diseases and suggests considering it in the differential diagnosis of acute polyarthritis. Moreover, our study highlights the uncommon but notable potential of B19V infection to induce persistent inflammatory responses requiring immunosuppressive therapy.

Large vessel vasculitis (LVV) in the elderly often prompts consideration of giant cell arteritis; however, mimickers must be carefully excluded. We report the case of a 70-year-old woman with constitutional symptoms, elevated inflammatory markers, and FDG-PET findings suggestive of LVV. Spontaneous clinical and laboratory improvement in the absence of immunosuppression raised suspicion for an alternative diagnosis. Further evaluation revealed positive treponemal serology, and syphilitic aortitis was confirmed. Treatment with penicillin led to complete resolution of vascular inflammation. This case highlights the importance of considering infectious mimics, such as syphilis, in atypical or self-resolving presentations of LVV, particularly in elderly patients.