Risk factors for cervical spine instability in patients with rheumatoid arthritis

Introduction Cervical spine (C-spine) instability is a unique and significant characteristic of rheumatoid arthritis (RA) because its occurrence is not rare and it can cause compressive cervical myelopathy, which may lead to serious neurologic sequelae. This study evaluated the prevalence and risk factors of C-spine instabilities in RA patients with a focus on anti-citrullinated protein antibody (ACPA) and biologic disease-modifying antirheumatic drug (DMARD) therapies. Methods The presence of C-spine instabilities in 1114 patients with RA was evaluated using C-spine radiographies according to the defined metrics. Multivariable logistic regression analyses were performed to identify independent predictors of C-spine instability. The initiation of biologic DMARDs was assessed via a Kaplan-Meier analysis and compared using log-rank tests. Results In total, 306 (27.5%) patients presented with C-spine instabilities. The most common type was atlantoaxial subluxation (AAS; n = 199 [17.9%]). Male sex, positivity for rheumatoid factor and ACPA, erosive change in the peripheral joints, and presence of osteoporosis were independently associated with C-spine instabilities (all P < 0.05). In particular, positivity for ACPA was the most powerful risk factor (odds ratio: 2.33 [95% confidence interval: 1.37, 3.96], P = 0.002), and it was closely associated with AAS. Patients with AAS were at a higher risk for early initiation of biologic DMARDs. Conclusions Positivity for ACPA was a significant risk factor for C-spine instability, and AAS was remarkably correlated to the early initiation of biologic DMARDs, a surrogate index of poor long-term outcomes.