Accelerated Development of Cervical Spine Instabilities in Rheumatoid Arthritis: A Prospective Minimum 5-Year Cohort Study

OBJECTIVE To clarify the incidence and predictive risk factors of cervical spine instabilities which may induce compression myelopathy in patients with rheumatoid arthritis (RA). METHODS Three types of cervical spine instability were radiographically categorized into "moderate" and "severe" based on atlantoaxial subluxation (AAS: atlantodental interval >3 mm versus ≥10 mm), vertical subluxation (VS: Ranawat value <13 mm versus ≤10 mm), and subaxial subluxation (SAS: irreducible translation ≥2 mm versus ≥4 mm or at multiple). 228 "definite" or "classical" RA patients (140 without instability and 88 with "moderate" instability) were prospectively followed for >5 years. The endpoint incidence of "severe" instabilities and predictors for "severe" instability were determined. RESULTS Patients with baseline "moderate" instability, including all sub-groups (AAS(+) [VS(-) SAS(-)], VS(+) [SAS(-) AAS(±)], and SAS(+) [AAS(±) VS(±)]), developed "severe" instabilities more frequently (33.3% with AAS(+), 75.0% with VS(+), and 42.9% with SAS(+)) than those initially without instability (12.9%; p<0.003, p<0.003, and p = 0.061, respectively). The incidence of cervical canal stenosis and/or basilar invagination was also higher in patients with initial instability (17.5% with AAS(+), 37.5% with VS(+), and 14.3% with SAS(+)) than in those without instability (7.1%; p = 0.028, p<0.003, and p = 0.427, respectively). Multivariable logistic regression analysis identified corticosteroid administration, Steinbrocker stage III or IV at baseline, mutilating changes at baseline, and the development of mutilans during the follow-up period correlated with the progression to "severe" instability (p<0.05). CONCLUSIONS This prospective cohort study demonstrates accelerated development of cervical spine involvement in RA patients with pre-existing instability--especially VS. Advanced peripheral erosiveness and concomitant corticosteroid treatment are indicators for poor prognosis of the cervical spine in RA.