A67: Factors That Contribute to Classification of Children as Having Undifferentiated Juvenile Idiopathic Arthritis
Authors: Mercedes O. Chan, Ross E. Petty, Kiem Oen, Ciarán M. Duffy, Lori B. Tucker, Rae SM Yeung, Jaime Guzman
Journal: Arthritis & Rheumatology (2014)

Background/Purpose:

According to the ILAR criteria, undifferentiated juvenile idiopathic arthritis (U-JIA) includes children who fail to meet criteria for 1 of the other 6 categories or who meet criteria in more than 1 category. Classification requires category-specific application of 5 exclusion criteria: 1. Psoriasis in the patient or a 1st degree relative; 2. Arthritis beginning after the 6th birthday in an HLA-B27 + male; 3. HLAB27 associated disease in a 1st degree relative; 4. Rheumatoid factor positivity (RF+) on 2 occasions; and 5. The presence of systemic JIA (SoJIA).



A pilot single-centre study (n=21) revealed that psoriasis in a 1st degree relative was the most common reason for classifying patients as U-JIA; disregarding this criterion would allow re-classification of most U-JIA patients and had no impact on the classification of JPsA patients (Chan et al., 2011). We aimed to determine the most frequent reasons for classifying children as U-JIA from a large multicenter prospective cohort of children with JIA (n=1104).



Methods:

Two investigators reviewed data on patients diagnosed with UJIA extracted from the Research in Arthritis in Canadian Children emphasizing Outcomes (ReACCh-Out) database. They identified by consensus the reasons for classifying patients as U-JIA and the JIA category they would fall in if the following two changes were made: disregarding psoriasis in a 1st degree relative, considering patients as RF negative when only a single positive RF test was recorded.



Results:

84 patients (51 female), were classified as U-JIA for the reasons shown in the 1.


Table 1. 	Exclusion criteria	1st degree relative with psoriasis (n=57)	B27 male>6 years + arthritis (n=4)	RF+ on 2 occasions (n=1)	RF+ on 1 occasion only (n=17)	1st degree relative with B27 related disease (n=4)	SoJIA (n=0)	Fulfills criteria for 2 categories (n=2)
Revised category if exclusion criteria disregarded	
Oligo	25	 	 	9	2	 	 	
Poly RF−	13	 	 	 	2	 	 	
Poly RF+	5 (1 RF+x2, 4 RF+x1)	 	 	 	 	 	 	
ERA	12	 	 	5	 	 	 	
Systemic	2	 	 	1	 	 	 	
JPsA	 	4	 	1	 	 	 	
U-JIA	 	 	1	1	 	 	2 (JPsA + ERA)	



If the criterion of having a 1st degree relative with psoriasis was disregarded, 25 patients would be classified as oligo JIA, 13 poly RF−, 5 poly RF+, 12 ERA and 2 SoJIA. If a single positive RF test was considered to be insufficient to meet the ILAR criterion of RF positivity, 9 patients would be re-classified as oligo JIA, 5 ERA, 1 SoJIA, 1 JPsA and 1 would remain U-JIA.



Conclusion:

Psoriasis in a 1st degree relative is the most common factor contributing to the classification of a child as having U-JIA and removing it from the existing criteria should be considered. The presence of a single positive test for RF was the second most common reason resulting in a classification of U-JIA. Definitive RF testing (two tests) should be maintained to satisfy the criterion of “RF positivity”.