Study question

In patients with psoriasis, what are the clinical predictors for psoriatic arthritis?

Study design

Design:

incidence cohort study with ⩽30 years of follow-up (20 936 person-years).

Setting:

Olmsted County, Minnesota, USA.

Patients:

1593 patients who were 18–98 years of age (mean age 43 y, 50% women), had a first diagnosis of psoriasis (plaque psoriasis 79%, guttate psoriasis 8.2%, sebopsoriasis 5.4%, and pustular psoriasis 3.3%), and did not have psoriatic arthritis at baseline.

Prognostic factors:

demographics, type of psoriasis, site of psoriasis, number of affected sites, and nail dystrophy.

Outcomes:

psoriatic arthritis, defined as a score ⩾3 on the following CASPAR criteria: (1) current psoriasis (2 points) or personal or family history of psoriasis; (2) nail dystrophy, such as onycholysis, pitting, or hyperkeratosis; (3) negative RF; …