Risk factors associated with having psoriatic arthritis in patients with cutaneous psoriasis.

The aim of this study was to determine if the following characteristics were associated with the presence of psoriatic arthritis in a sample of psoriasis patients: race, family history of psoriasis and psoriatic arthritis, age of onset of psoriasis, smoking, alcohol consumption and the maximum body surface area (BSA) affected by psoriasis. This was a case-control study involving 400 psoriasis patients who attended the Psoriasis and Photo-medicine clinic in the National Skin Center of Singapore over a 1-year period. Cases were psoriasis patients with psoriatic arthritis while controls were psoriasis patients without psoriatic arthritis. The diagnosis of psoriatic arthritis was made by rheumatologists and participants completed a self-administered standardized questionnaire. The maximum BSA involved was determined from the case notes. Psoriatic arthritis was not significantly associated with sex, race, age of onset of psoriasis, a family history of psoriasis, smoking and alcohol consumption but was significantly associated with a family history of psoriatic arthritis (P < 0.001) and the maximum body surface involved (P = 0.05). Using multivariate analysis to control for variables, the presence of psoriatic arthritis was significantly associated with a family history of psoriatic arthritis (odds ratio [OR] = 20.5; 95% confidence interval [CI] = 2.49-169.10) and the maximum BSA involved (OR = 2.52; 95% CI = 1.33-4.75). Indian psoriatic patients were more likely to have psoriatic arthritis compared to the other races. A family history of psoriatic arthritis and a greater maximum body surface involved may be associated with having psoriatic arthritis in this study population of psoriasis patients.