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Juvenile Arthritis Classification Criteria Compared In Nordic Study

Comparison of the proposed new and older classification criteria for juvenile idiopathic arthritis is complicated by the differing operational definitions they use of the subvariables.

Using the new ILAR rather than EULAR criteria, the number of cases with juvenile arthritis increases by 10 percent, considering the first half-year after onset.

However, validity of the ILAR criteria is low; these criteria frequently exclude patients from subgroup classification, and the possibility of having more than one diagnosis is not negligible. Furthermore, specified exclusion criteria for some of the subgroups are difficult to fulfill in clinical work, and the variables involved are questionable in terms of their consistency.

Construct validity of the two sets of criteria refers to how closely the two instruments are related and how each operates in classifying subgroups/categories.

The proposed new criteria (ILAR) are more descriptive than those formerly used [American College of Rheumatology (ACR), European League Against Rheumatism (EULAR)] but require validation against classifications already in use. This research group validated the ILAR in relation to the EULAR criteria and analysed their feasibility.

In the study, 20 doctors in five Nordic countries collected data from the incidence cases within their catchment areas over an 18-month period beginning July 1, 1997. Clinical and serological data from the first year of disease were collected. A total of 322 patients were included.

Classification by the ILAR criteria was possible in 321 patients; 290 patients had a disease duration of three months or less and were classified according to the EULAR criteria. One child could only be classified according to the EULAR criteria.

Thus, 31 of 322 children (9.6 percent) were classified according to the ILAR criteria only. Forty-eight of 321 patients (15 percent) did not fit any category, and 6 percent (20 of 321) fulfilled criteria for two categories.

In the ILAR classification, five of seven categories/subgroups have two to five specified exclusion criteria that highly discriminate the definition of each patient.

In this study, the exclusion criteria were fulfilled to only a small extent.

Study author is Lillemor Berntson and colleagues for the Nordic Study Group following a population-based incidence study in the Nordic countries of the construct validity of the EULAR and ILAR criteria in juvenile idiopathic arthritis.
J Rheumatol 2001;28:2737-43. "Construct Validity of ILAR and EULAR Criteria in Juvenile Idiopathic Arthritis: A Population Based Incidence Study from the Nordic Countries"

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