Psoriatic Arthritis Before Psoriasis: Patient Characteristics and Transition Rate

Objectives Psoriatic arthritis (PsA) is a heterogeneous inflammatory disorder affecting skin and multiple musculoskeletal domains. While cutaneous psoriasis precedes arthritis in most patients, approximately 7-15% of PsA patients are diagnosed prior to the onset of psoriasis. This statistic was identified based on UK registry data,[1] and few studies have corroborated the estimate, nor further characterized this patient subset. We aim to characterize the baseline characteristics of patients presenting with PsA prior to psoriasis, determine the incidence of psoriasis after PsA diagnosis and factors contributing to risk of psoriasis after PsA. Methods This is a retrospective analysis of prospectively collected data from the Gladman-Krembil Psoriatic Arthritis Program cohort, with an enrollment of 1689 PsA patients at the time of the study, all of whom were diagnosed with PsA and meet CASPAR criteria. Subjects with an onset of PsA preceding psoriasis at cohort entry, or those with no known psoriasis, were identified. The latter underwent a chart review to identify the time of psoriasis onset. Baseline characteristics were then compared to the rest of the cohort, who had a psoriasis onset preceding or simultaneous with PsA. A multivariate Cox regression of time-independent covariates was used to identify factors influencing the incidence of psoriasis after PsA. Results 116 total patients were identified; 29 did not have known psoriasis at cohort entry and the remainder had established PsA preceding psoriasis at cohort entry. The incidence of psoriasis following PsA is 9.2 cases per 100 person-years; however, the incidence reduced over time. Compared to PsA after psoriasis, patient with PsA before psoriasis were younger at PsA diagnosis (35.69 years vs 38.86 years, p≤0.017) (Table 1), less likely to have nail involvement (43.0% vs 65.7%, p≤0.001), more likely to have erosions (68.9% vs 51.6%, p=0.001) and more radiographic damage at presentation (Modified Steinbrocker score 4.00 vs 2.00, p≤0.001). In the multivariate Cox regression model, use of bDMARD (HR 0.24, 95% CI [0.11-0.53], p ≤0.001) or NSAIDs (HR 0.54, 95% CI [0.35-0.90], p=0.017) was associated with a lower risk of psoriasis. Male sex was associated with a higher risk of psoriasis (HR 1.67, 95% CI [1.07-2.62], p=0.024). Table 1. Baseline Characteristics at Cohort Entry of Patient Presenting with Psoriasis Before or Concurrent to Psoriatic arthritis, to Those Presenting with Psoriatic Arthritis before Psoriasis. Conclusion Patients presenting with PsA prior to onset of psoriasis are younger at PsA diagnosis and more likely to sustain joint damage. This could suggest the absence of psoriasis leads to delayed diagnosis and treatment. The use of bDMARDs or NSAIDS, but not cDMARDs was associated with reduced risk of psoriasis after PsA. [1.] Tillett W. Rheumatology 2017;56:2109-13.

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