Small joint involvement in psoriatic arthritis is associated with onycholysis: the Reykjavik Psoriatic Arthritis Study

Objectives: Psoriasis and psoriatic arthritis (PsA) are associated with nail changes. Recent reports suggest that nail changes may be a part of the enthesitis of PsA and that they predict the onset of arthritis among patients with psoriasis, but they have not reported on subclasses of nail changes. However, earlier reports suggested that onycholysis is the nail change most strongly associated with PsA. If nail changes in PsA are a sign of enthesitis, they might be associated with small joint disease in general and the objective of this study was to test this hypothesis. Methods: A total of 154 patients recruited through the Reykjavik Psoriatic Arthritis Study had a joint, skin, and nail evaluation. Associations with small joint disease were tested using univariate analysis, and confirmed in a multivariate model. Results: Onycholysis had a strong association with small joint involvement [odds ratio (OR) 3.42, 95% confidence interval (CI) 1.41-8.92], while other types of nail changes did not. The number of swollen joints and shorter disease duration were also associated with small joint disease. Conclusions: Onycholysis is associated with small joint disease in PsA. Future studies of PsA should report the subtypes of nail changes. Longitudinal studies are needed to determine whether onycholysis predicts PsA.