Patterns of joint involvement at onset differentiate oligoarticular juvenile psoriatic arthritis from pauciarticular juvenile rheumatoid arthritis.

OBJECTIVE: To compare the patterns of joint involvement of patients with oligoarticular onset juvenile psoriatic arthritis (Oligo-JPsA) and pauciarticular onset juvenile rheumatoid arthritis (Pauci-JRA) in order to estimate the predictive performance of specific patterns for the diagnosis of Oligo-JPsA.

METHODS: Twenty-three children who fulfilled the diagnostic criteria for JPsA (Vancouver criteria) and who had fewer than 5 joints involved in the first 6 months of disease (Oligo-JPsA), and 64 children with Pauci-JRA (ACR criteria) were enrolled. Patients were also classified with respect to the ILAR criteria for juvenile idiopathic arthritis (JIA). Patient characteristics and clinical features at onset and during followup were determined. Patterns of joint involvement at onset of disease and their ability to differentiate between Oligo-JPsA and Pauci-JRA/Oligo-JIA were evaluated.

RESULTS: Small joint disease (defined as involvement of any of the metatarsophalangeal or proximal or distal interphalangeal joints of the foot, or metacarpophalangeal or proximal or distal interphalangeal joints of the hand) was significantly more frequent in Oligo-JPsA than in Pauci-JRA at disease onset. The odds of patients with Oligo-JPsA having small joint disease or wrist disease within 6 months of disease onset were much higher than those with Pauci-JRA or Oligo-JIA (p < 0.05 or 0.001).

CONCLUSION: Small joint disease and wrist disease are suggestive of Oligo-JPsA. The use of a criterion consisting of small joint disease and/or wrist disease and/or dactylitis instead of dactylitis alone may increase the ability to differentiate Oligo-JPsA from Pauci-JRA or Oligo-JIA.