Psoriatic arthritis and onycholysis -- results from the cross-sectional Reykjavik psoriatic arthritis study.

Objective: To measure the associations between subtypes of nail changes and psoriatic arthritis (PsA) among patients with psoriasis.

Methods: Patients age 18 years and older with active psoriasis were examined for skin and nail changes and asked if they had been diagnosed with PsA. Patients with arthritis were invited for a separate study 1-6 years after their initial visit. Univariate and multivariate analyses were used to test the strength of associations between subtypes of nail changes and arthritis.

Results: Of 1116 patients with psoriasis, 37% (95% CI 34%-40%) had nail changes. Age, any nail change, onycholysis, and pitting were each associated with PsA on univariate analysis. Multivariate analysis showed that onycholysis was the only type of nail change independently associated with PsA (OR 2.05, p < 0.001). Nail changes persisted and had increased in prevalence at the followup examination at a mean of 3.8 (median 4 yrs, interquartile range 3-4) years later. Previously reported associations between psoriasis location and arthritis were not seen in this dataset.

Conclusion: PsA is associated with onycholysis. Associations with pitting and subungual hyperkeratosis were not statistically significant. Subtypes of nail changes should be analyzed separately in future studies of PsA.