Atlantoaxial instability in psoriatic arthritis: Frequency and correlated factors from a single-center cohort

OBJECTIVES: There is very limited data regarding atlantoaxial instability (AAI) in patients with psoriatic arthritis (axPsA). In this study, we aimed to contribute to the existing literature on this topic. METHODS: Adult patients were included in this single-center study who were classified as PsA by the 'CASPAR' criteria and evaluated as having axial involvement according to the 'Calin' criteria. Those with inflammatory or non-inflammatory diseases that could affect the spine were excluded. Electronic patient files were reviewed retrospectively. Lateral neutral/full extension/full flexion and open-mouth anteroposterior cervical radiographs were evaluated by three rheumatologists blinded to the patients. Patients were compared in two groups as AAI-positive and AAI-negative. RESULTS: A total of 100 patients with a mean age of 48.8 years and a mean PsA duration of 7.4 years, 57% of whom were female, were included in the study. A total of 20 AAI lesions were detected in 18% patients; subaxial subluxation was detected in eight, anterior atlantoaxial subluxation (AAS) in seven, posterior AAS in three, lateral AAS in one, and vertical subluxation in one case. In the group with AAI, the presence of psoriasis (Ps) (p = 0.037), scalp psoriasis (p < 0.001), and the use of targeted therapy for Ps and PsA (p < 0.001, p < 0.001) were significantly higher than in the AAI-negative group. CONCLUSION: Given that Ps and PsA patients on targeted therapy may reflect cases with higher disease activity and inadequate response to conventional treatments, it may be appropriate to consider closer monitoring for AAI in these patients. Key Points • Atlantoaxial instability is present in approximately one-fifth of patients with axial psoriatic arthritis. • The most common instability lesion is subaxial subluxation, accounting for 40% of all lesions. • The presence of psoriasis, scalp psoriasis, and the use of targeted therapies for psoriatic arthritis or psoriasis are significantly more frequent in the group with atlantoaxial instability. These factors may be useful for cervical spine monitoring in patients with axial psoriatic arthritis. • The use of targeted therapies for psoriatic arthritis or psoriasis may indirectly indicate an association between high disease activity and atlantoaxial instability.