Epidemiological analysis of psoriatic arthritis patients in Japan

To determine the current status of psoriatic arthritis, we conducted a retrospective survey by sending questionnaires. The newly visited psoriatic arthritis patients accounted for 10.5% (95% confidence interval, 7.9-13%) of all newly visited psoriasis patients (n = 2581) between April 2014 and March 2015 in 73 institutes. Additionally, questionnaires on detailed patients' information were returned by 92 institutes (response rate, 70.8%), where 1282 patients with psoriatic arthritis were identified. There was a male predominance. The mean onset age of psoriatic arthritis was 44.9 years, and mean onset age for cutaneous psoriasis (36.4 years) was lower than that for arthritis (45.1 years). The mean duration in patients who developed psoriasis prior to arthritis was 11.2 years, while that in patients preceded by arthritis was 4.4 years. According to the Moll and Wright criteria, polyarthritis type was most common (36%), followed by distal interphalangeal type (26%) and oligoarthritis type (22%). Peripheral joint pain was 61.5%, back pain such as lumbago and neck pain was 34.3%. Enthesitis and dactylitis were observed in 28.3% and 59.2%, respectively. Biologics were used in 55.5% of psoriatic arthritis patients, and 31% used disease-modifying antirheumatic drugs. In conclusion, the ratio of psoriatic arthritis in Japan is increasing, and nearly 10% of new psoriasis patients had psoriatic arthritis. This study shows the current status of psoriatic arthritis in Japan, including several unexpected findings such as male predominance, longer duration between the onset of cutaneous psoriasis and arthritis, and dominance of polyarthritis.