An Atypical Presentation of Seronegative Rheumatoid Arthritis.

The American College of Rheumatology/European League Against Rheumatism (ACR/EULAR) 1987 classification for rheumatoid arthritis (RA) focuses on four main clinical findings without emphasizing biomarker serology. On the other hand, the updated ACR/EULAR 2010 classification relies more on acute-phase reactants and biomarker serology. While a positive rheumatoid factor (RF) and positive anti-citrullinated protein antibody (ACPA) are specific for RA, at least 15%-25% of patients are seronegative. Given that the ACR/EULAR 2010 classification is more likely to miss these seronegative patients, clinical judgment is important while assessing patients to avoid delays in diagnosis and onset of treatment.