Epidemiology and clinical pattern of psoriatic arthritis in Germany: a prospective interdisciplinary epidemiological study of 1511 patients with plaque-type psoriasis

Background  Because psoriatic arthritis (PsA) usually develops years after the first manifestation of skin symptoms, in many cases the initial diagnosis of PsA depends on the dermatologist.
Objectives  To investigate the prevalence and clinical pattern of PsA in a daily practice population of patients with psoriasis.
Methods  Patients were enrolled in an observational prospective cross-sectional cohort study at 48 community and academic centres. Demographic and medical parameters were recorded, including severity of skin symptoms (Psoriasis Area and Severity Index, PASI), previous and current treatments, concomitant diseases, and the impact of psoriasis on productivity and health-related quality of life (Dermatology Life Quality Index, DLQI). Patients with joint symptoms were referred to a rheumatologist for diagnosis and to record the activity and pattern of arthritis.
Results  Among 1511 patients 20·6% had PsA; in 85% of the cases PsA was newly diagnosed. Of these patients more than 95% had active arthritis and 53·0% had five or more joints affected. Polyarthritis (58·7%) was the most common manifestation pattern, followed by oligoarthritis (31·6%) and arthritis mutilans (4·9%). Distal interphalangeal involvement was present in 41·0% and dactylitis in 23·7% of the patients. Compared with patients without arthritis, patients with PsA had more severe skin symptoms (mean PASI 14·3 vs. 11·5), a lower quality of life (mean DLQI 11·6 vs. 7·7) and greater impairment of productivity parameters.
Conclusions  The findings are consistent with a high prevalence of undiagnosed cases of active PsA among patients with psoriasis seen by dermatologists. As many of these patients also have significant skin symptoms, treatment strategies are required that are equally effective in the control of skin and joint symptoms of psoriasis.