Incidence of psoriatic arthritis in a UK primary care psoriasis population

OBJECTIVE: To determine the annual incidence of psoriatic arthritis in a UK primary care population with preexisting psoriasis followed prospectively over two years after excluding baseline prevalence of existing disease.

METHODS: TUDOR (Total bUrDen of psORiasis) was a multi-centre, prospective, two-arm parallel-group cluster randomised controlled trial of the early identification of PsA by annual rheumatological assessment (termed Enhanced Surveillance) versus standard care in people with psoriasis identified in primary care. Incidence of psoriatic arthritis is reported at 12- and 24-months using patients from the Enhanced Surveillance arm, which allows the exclusion of patients with prevalent PsA at baseline.

RESULTS: Fourteen of 511 participants attending a 12-month screen developed PsA over that interval giving an incidence of 2.74 per 100 patient years (p-yrs) (95% CI: 1.32 to 4.16) and another 7 of 444 participants attending the 24-month visit developed PsA giving an incidence of 1.58 per 100 p-yrs (95% CI: 0.42 to 2.74). The combined incidence over 2 years was 2.20 per 100 p-yrs (95% CI: 1.27 to 3.13).

CONCLUSION: The estimated annual incidence of PsA over a 2-year period was 2.20 per 100 p-yrs, that is in keeping with a higher incidence of PsA than that found when relying on health records alone. Extended follow-up of the TUDOR cohort with accrual of larger numbers of incident cases will allow risk factors for psoriatic arthritis to be explored in more depth.