Epidemiology of psoriatic arthritis.

Research into psoriatic arthritis continues to be hampered by the lack of a validated case-definition. There may be progress toward consensus with a new data-derived diagnostic classification criteria set recently reported and a current international project aiming to firmly validate criteria. Statistical techniques such as latent class analysis may permit a comparison of the accuracy of competing criteria sets, in the absence of a gold standard for diagnosis. Genetic studies are inconclusive, but ethnic differences in disease expression suggest a definite genetic role. Recent community-based research suggests an incidence rate of about 6/100,000 per annum, and a prevalence of about 1/1000. Clinic-based disease may be associated with increased mortality, whereas community based disease is not. The development of internationally accepted criteria for the diagnosis of psoriatic arthritis will be a major impetus towards research into this complex disease.