Epidemiological and clinical characteristics of psoriatic arthritis in northern Norway

Abstract

Background: To determine the characteristics of psoriatic arthritis (PsA) in northern Norway, where the human leucocyte antigen HLA‐B27 is prevalent. Methods: An observational study of patients with ICD‐9 CR codes for psoriatic arthropathy (696.0 and 713.3) and spondylarthritis (720) seen during a 19‐year period at a single regional rheumatology department. In patients with confirmed PsA demographics, date of onset of arthritis and psoriasis, clinical presentation and subsequent disease course (including therapeutic measures) were recorded during a mean follow‐up of 11.1 years. Results: Arthritis was documented in 329/657 (50%) of patients with a diagnostic code for PsA. The mean annual incidence rate for PsA was 6.9/100 000 and the point prevalence was 130/100 000 (0.13%) adults. The male to female ratio was 1.4 and the mean age at onset of psoriasis was 27.8 years (SD 14.1), and 35 years (SD 11.8) at onset of arthritis. Arthritis preceded psoriasis in 13.8% of cases. Oligoarthritis was the most frequent subtype (48%), followed by polyarthritis (32%), spondylitis (9%), monoarthritis (7%), and classic distal interphalangeal (DIP) arthritis (2%). Erosive disease (56% of cases) occurred mainly with polyarthritis; arthritis mutilans occurred in six patients (2%). Surgical interventions were performed in 22% of patients. Disease activity fluctuated considerably over time. Mortality (4.3%) was increased in PsA patients with polyarthritis and secondary amyloidosis (n = 5). Conclusion: The prevalence of PsA and related spondylitis is not increased in northern Norway. PsA does, however, lead to a considerable burden of disease due to erosive disease development and surgical intervention.