Anti-cyclic Citrullinated Peptide Antibody: A Key Predictor for Rheumatoid Arthritis in Undifferentiated Arthritis
Introduction
Undifferentiated arthritis (UA) is a common form of inflammatory arthritis that can’t be diagnosed as a specific rheumatic disease. While nearly half of UA patients achieve remission without treatment, less than half eventually develop rheumatoid arthritis (RA). Early prediction of RA in UA patients is crucial for appropriate intervention. This study aimed to identify predictors of RA in UA patients.
Methods
Study Design
A prospective, multi-center study was conducted from January 2013 to October 2016 among Chinese patients with UA in 22 tertiary-care hospitals. Clinical and serological parameters were collected at recruitment, and patients were followed up every 12 weeks for 2 years. Multivariate Cox proportional hazards regression was used to identify predictive factors.
Patients
Inclusion criteria: patients aged >18 years with persistent arthritis ≥6 weeks and ≤24 weeks, no treatment with glucocorticoids, DMARDs, or biologic agents. Exclusion criteria: pregnant patients, those with uncontrolled hypertension, abnormal heart, liver, or renal function, and alcohol addiction.
Data Collection and Analysis
Demographic, clinical, and laboratory data were entered into a database. Statistical analysis included Student’s t test, Mann-Whitney U test, and Cox proportional hazards regression.
Results
Baseline Characteristics
A total of 234 patients were recruited, with 217 completing the study. Most patients had morning stiffness, and the most affected joints were proximal interphalangeal and wrist. RF and anti-CCP antibody positivity rates were 19.4% and 16.1%, respectively.
Diagnosis after Follow-up
83 (38.2%) patients went into remission. 20 (9.2%) developed RA, 10 (4.6%) OA, 2 (0.9%) PsA, and 1 (0.5%) each of SLE, dermatomyositis, Rhupus syndrome, and ReA.
Predictive Factors of RA
UA patients who developed RA had higher RF-positivity (42.9% vs. 16.8%, P = 0.008), anti-CCP antibody-positivity (66.7% vs. 10.7%, P < 0.001), and double-positivity rate of RF and anti-CCP antibody (38.1% vs. 4.1%, P < 0.001). Anti-CCP antibody (hazard ratio 18.017, 95% confidence interval: 5.803–55.938, P < 0.001) was an independent predictor for RA development.
Discussion
RF and Anti-CCP Antibody
RF positivity was a risk factor in some studies but not in this one. However, testing for RF in clinics can increase UA diagnosis sensitivity. Anti-CCP antibody is controversial but is a key predictor in this study. It is easy to test and can predict RA development in UA patients.
Other Factors
Smoking and periodontitis were not predictors in this study, possibly due to low prevalence. Early DMARD treatment can prevent UA development, but this study did not include it.
Conclusion
Only a small proportion of UA patients progress to RA. Anti-CCP antibody should be tested in all UA patients at disease onset. Positive patients should be treated with DMARDs to prevent RA.
This study provides valuable insights into predicting RA in UA patients. Further research is needed to confirm these findings and explore the role of early treatment.
doi:10.1097/CM9.0000000000000570
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