Growing up with chronic arthritis: the confusing matter of classification

Correspondence to Ellen Nordal; [email protected] Disease classification in rheumatology is a matter of debate, in paediatrics between International League Against Rheumatism (ILAR) classification ‘pros and cons’, as well as between paediatric and adult rheumatologists. Indeed, there is no consensus yet about how we should name the disease of adults with juvenile idiopathic arthritis ( JIA) in childhood. The non-concordance of adult and paediatric classifications for chronic inflammatory rheumatic diseases is confusing for caregivers, and above all for our patients. Will they be ‘lost in transition’, as phrased by McDonagh and Viner, when their disease stays the same, but gets a new name? Will their treatment be modified according to this new name and the corresponding recommendations for adult disease management? Yes, it is definitely time to think about a thorough modification of the ILAR categories of childhood chronic arthritis. The ILAR agreed on a classification that comprises all types of idiopathic arthritis in children under the umbrella term of JIA, subdivided into seven categories comprising the systemic, oligoarticular, rheumatoid factor (RF)-negative polyarticular, RF-positive polyarticular, juvenile psoriatic arthritis ( jPsA), enthesitis-related arthritis (ERA) and the undifferentiated form. This was the first time that Europeans and Americans agreed to speak the same language. However, since launched, the ILAR classification has been regularly criticised. It was revised in 2001, and the reduced emphasis on heredity resulted in a significant decrease in the rates of children with undifferentiated arthritis. Calls for further modifications are nevertheless still numerous. Martini recognised that dividing patients into groups according to the number of joints involved at disease onset (oligoarticular/polyarticular JIA) was not gathering homogeneous categories; others claimed that strict exclusion criteria of the present classification excluded many authentic juvenile spondyloarthritides from the ERA category, 10 the same for the jPsA category, 12 and even the RF-positive polyarticular category. The undifferentiated arthritis group varies markedly in frequency in different reports, because it depends on thorough work-up on heredity and other exclusion criteria. 15 Contrary to the intentions of the ILAR, the undifferentiated group in follow-up tends to increase instead of decrease over time. A new proposal is emerging from Martini and colleagues to define a group composed of young children ≤6 years of age with arthritis and presence of antinuclear antibodies (ANA). Indeed, two important papers from their team showed that the clinical characteristics of ANA-positive young children during the first 2 years after disease onset were very similar despite being classified into different ILAR categories, that is, RF-negative polyarticular, oligoarticular (persistent and extended), jPsA and undifferentiated arthritis, proving at the same time how heterogeneous these categories are. 17 However, there are several concerns. First, we have pointed out that the ANA immunofluorescence test is operatordependent and still not consensual in terms of threshold of positivity in different laboratories worldwide, even though the aforementioned studies define ANA positivity as two positive immunofluorescence tests at a titre of ≥1/160 on Human Epithelial type 2 (HEp-2) cells at least 3 months apart. 17 Second, ANA in JIA still have no identified biological target, and therefore no clear link to aetiology, pathophysiology or treatment option. Most importantly, prospective long-term follow-up of young children with ANA-positive JIA from different cohorts and geographical regions is still lacking. Therefore, ANA should not in our opinion be a classification determinant until more standardisation and evidence for relevance in treatment, disease course or outcome is available. The clinical entity of psoriatic arthritis (PsA) versus enthesitis and spondyloarthritis