Juvenile Psoriatic Arthritis: Bathwater or Baby?

Abstract

Arthritis in children represents a markedly heterogeneous family of conditions. To get a handle on this complexity, pediatric rheumatologists have developed an evolving set of classification criteria. The most recent iteration of the juvenile idiopathic arthritis (JIA) nomenclature recognizes 7 subgroups defined on the basis of compelling features of the clinical phenotype, supported in some cases by laboratory tests such as rheumatoid factor or HLA-B271. One of these subgroups is juvenile psoriatic arthritis (JPsA), which may be diagnosed in children with arthritis (1) in the presence of psoriasis, or (2) in the absence of psoriasis, if 2 features suggestive of a psoriatic diathesis are present, including dactylitis, nail changes, or psoriasis in a first-degree relative, all in the absence of specified exclusions. Unfortunately, the differentiation of psoriatic from non-psoriatic arthritis in children is challenging. In about half of children with JPsA, the classic rash presents after the onset of arthritis, with a lag time that may be 10 years or more2. Manifestations of psoriasis in the young child are often atypical or incompletely specific, such as erythema and scale behind the ears, features taken into consideration by an earlier (Vancouver) set of JPsA criteria but excluded under the JIA nomenclature3. Even in cases where evidence for psoriasis is unambiguous, it remains an open question whether psoriasis is relevant to proper categorization of the child with arthritis. Is JPsA sufficiently distinct from other forms of JIA to merit its own category? In this issue of The Journal, Butbul and colleagues examine this question from a practical vantage point4. They ask: Do patients meeting JIA criteria for JPsA exhibit a different phenotype and outcome from patients who do not? To answer this question, they identified about half the patients with JPsA followed at the … Address correspondence to Dr. Nigrovic. E-mail: pnigrovic{at}partners.org