Psoriatic arthritis in Reykjavik, Iceland: prevalence, demographics, and disease course

OBJECTIVE: To determine the prevalence, demographics, and course of psoriatic arthritis (PsA) in the Reykjavik area of Iceland. METHODS: In total 220 patients >/= 18 years of age living in the Reykjavik area of Iceland were located in a community registry of psoriatic patients and in hospital records. Of these, 156 (71%) were interviewed and examined for verification of skin and joint disease according to published criteria. RESULTS: Prevalence of PsA in the adult population was estimated to be 164 per 100,000 (95% CI 143-187), adjusted to 139 per 100,000 (95% CI 112-169) after exclusion of 25 individuals. The female to male ratio was close to 2:1. The mean age at skin disease onset was 23 years, with significantly earlier onset in women (age 20 yrs in women vs 26 yrs in men; p = 0.01), but there was no significant difference for age at the time of onset of joint disease. Mean duration of PsA was 20 years. Oligoarthritis was the most common (44%), followed by polyarthritis (31%), enthesitis (8%), and inflammatory back pain (7%). According to patients' recall of clinical features at onset, 78 patients (60%) had changed categories of PsA at the time of the study, most frequently from polyarthritis to oligoarthritis (48%), followed by oligoarthritis to polyarthritis (36%). These changes seemed independent of use of disease modifying drugs, which 54% had received. CONCLUSION: PsA in Reykjavik, Iceland, has a prevalence of at least 0.14% and is strikingly more common in women. The majority of patients reported a change in the pattern of affected joints during the course of their disease.