Introduction

Juvenile idiopathic arthritis (JIA) is the most common autoimmune condition in childhood, with a yearly incidence of 15 per 100,000 children in Nordic countries [1]. The International League of Associations for Rheumatology (ILAR) developed criteria to divide JIA into categories based on distinct clinical features and/or laboratory findings to identify homogeneous entities suitable for studies and guidance in clinic [2].

In recent years, the rationale for the ILAR criteria for JIA has been debated. It is felt that each of the subcategories still encounters heterogeneous conditions and the criteria may not be adequate for selecting homogeneous entities [3–8]. Antinuclear antibody (ANA) positivity can be found in all subtypes but is more frequent in patients with oligoarthritis and rheumatoid factor negative polyarthritis. The frequency of ANA positivity among oligoarticular patients has been reported between 61 and 75% [9, 10]. However, the antigenic specificity of the ANAs in JIA has not been elucidated, and no evidence of a role for ANAs in the pathophysiology has been demonstrated [11].

It has been hypothesized that ANA-positive patients irrespective of their underlying JIA subtype represent the same disease and it has been questioned whether patients with early onset disease and a positive ANA should be grouped as a separate category unrelated to the number of joints affected [7, 8, 12–14]. This is based on the fact that most ANA-positive patients are younger at age of onset, demonstrate a female predominance, predominantly have asymmetric arthritis, have a higher risk of developing uveitis, and show a lack of hip involvement [8]. The literature is not uniform concerning the number of affected joints during the disease course. In ANA-negative patients with polyarticular JIA Ravelli et al. found a greater cumulative number of affected joints over time [8]. On the other hand, Ma et al. reported a higher number of cumulative active joints among ANA-positive Japanese patients within the first year of the disease [14] and Guzman et al. reported an increased risk of flare associated with ANA positivity in a larger study in the ReACCh-Out cohort [15].

In the literature, evidence to support a separation based on ANA status is contradictory and depends heavily on the specific outcomes studied.

Therefore, the aim of this study was (1) to describe the characteristics of JIA patients based on their ANA status and (2) to compare remission and inactive disease rates based on ANA status.

Patients and methods

Patients

This was a single-center, retrospective study of children diagnosed with JIA at Aarhus University Hospital, Denmark, between January 2000 and May 2014. Patients were identified through the divisional database which includes all patients seen in the rheumatology clinic. Patients were included if they were diagnosed before the age of 16 years, fulfilled the ILAR criteria for JIA [2], ANA results were available, and had a follow-up of 1 year or more. ANA positivity was detected using indirect immunofluorescence (IIF) testing with Hep-2 cells as substrate [19]. ANA positivity was defined as at least two positive results with a titer of ≥1:160, with ANA tests performed at least 3 months apart. Patients with a follow-up of less than 1 year and with only one ANA test performed were excluded.

Demographic and clinical features

Demographic and clinical data were collected from the divisional database, paper charts, and electronic medical records. Demographic features included age at diagnosis, gender, age at disease presentation, number of active joints at diagnosis, presence of rheumatoid factor, ANA status, presence of uveitis, and medication during the disease course. Features at last follow-up included age at last visit, number of active joints, current medication, and remission status.

Remission

At last follow-up, remission status was defined by the Wallace preliminary criteria [16]. Remission on medication was defined as at least 6 continuous months of inactive disease on medication. Clinical remission off medication was defined as 12 months or more of inactive disease off all anti-rheumatic (and anti-uveitis) medication [16]. Inactive disease was defined as no active arthritis; no fever, rash, serositis, splenomegaly, or generalized lymphadenopathy attributable to JIA; no active uveitis; and normal erythrocyte sedimentation rate or C-reactive protein.

Statistical analysis

Descriptive statistics were reported as absolute numbers and frequencies for categorical variables and mean and standard deviation for continuous variables. Comparison analyses between two groups were performed by a t test. Categorical data were compared by Pearson’s Chi-square test. To determine independent factors for achieving remission, binary logistic regression analyses were performed. IBM SPSS Statistics, version 24 (IBM Corp, Armonk, NY, USA) was used for all analyses.

Results

Patients

A total of 685 patients with the diagnosis of JIA between January 2000 and May 2014 were identified in the divisional database. Two patients were excluded because of a wrong diagnosis (one with isolated uveitis, one with mixed connective tissue disease (MCTD)) and 58 patients because of insufficient data on ANA status. Six hundred twenty-five patients fulfilled ILAR criteria, had two recorded ANA tests and were followed for more than 1 year, and were included in this study. Of the included patients, 405 were female and 220 patients were male with a mean age at diagnosis of 98 months (Table 1) and mean disease duration 66.9 months (SD 36.9). The most common subtype was oligoarticular persistent JIA affecting 215 (34%) children, followed by polyarticular RF negative JIA affecting 125 (20%) children and oligoarticular extended JIA affecting 101 (16%) children. All patient demographic data can be found in Table 1.

Table 1 Demographic data of study population
Full size table

ANA positivity was present in 230 (37%) of all JIA patients, and ANA negativity in two thirds of patients (63%). There are significant differences between the two groups with a more pronounced female predominance in the ANA-positive group (p < 0.001) and a difference in subtype distribution. We found a significantly higher frequency of ANA positivity in oligoarticular JIA but a low frequency of positive ANA in systemic, psoriatic and undifferentiated JIA (Table 1). In the ANA-positive group, the most frequent subtype represented was the oligoarticular and polyarticular RF-negative subtypes.

ANA-positive patients had a significantly younger age at diagnosis than ANA-negative patients (Tables 1 and 2). No significant difference in active joint count either at diagnosis or at last follow-up was observed between ANA-positive and ANA-negative patients in the total JIA cohort (Table 2). Psoriatic JIA patients showed higher number of active joints at diagnosis in the ANA-positive group (p = 0.048). In all other subtypes, ANA-positive and ANA-negative patients had a similar average joint count at diagnosis. At last follow-up, the average joint counts were low in all subtypes and, irrespective of their ANA status, all subtypes had comparable average joint count (Table 2).

Table 2 t test of mean differences of “age at diagnosis” and “joint count at diagnosis” and at follow-up between patients with pos. or neg. ANA
Full size table

Almost 80% of patients were in remission on or off medication at their last follow-up appointment (Table 3), which was also resembled in the low average joint count at last follow-up (0.1 ± 0.459) with 93% of patients with no active joints (joint count = 0). More than half of the patients were in remission off medication for more than 12 months at last follow-up. We found no significant difference in the remission rate on or off medication between the ANA-positive and ANA-negative patients (Table 3). ANA-positive patients show a significant high risk for the presence of uveitis (OR = 7.8, p < 0.001) at one point during the course of the disease, and a low probability of HLA-B27 positivity (p = 0.046) (Table 3). At last follow-up, 41/625 patients had 1 or more active joints, without a significant difference in ANA-status (Table 3).

Table 3 Chi-square test of ANA-status and RF, HLA-B27, uveitis, and remission
Full size table

The likelihood of achieving remission on medication for at least 6 months or remission off medication for more than 12 months was not related to ANA or gender (Table 4). The likelihood of achieving remission off medication (for more than 12 months) was significantly less seen in RF-positive patients, in HLA-B27-positive patients, and in patients with uveitis at any time during the disease course (Table 4).

Table 4 Binary logistic regression analysis predicting likelihood of achieving remission on or off medication
Full size table

Discussion

To our knowledge, this is the first study to systematically evaluate remission on and off medication in JIA patients based on their ANA status.

As expected, in our study, ANA positivity was found to be associated with younger age at onset, female predominance, oligoarticular subtypes, and presence of uveitis at any time during the disease course. These findings indicate the generalisability of the cohort, as it closely resembles what is found in the literature [1, 2, 17].

This study shows that remission rates are not significantly different based on ANA positivity. Recently, questions have been posed if ANA positivity should lead to a different classification, where ANA positivity weighs heavily towards certain categories [7, 8, 12–14]. Our study clearly shows that ANA positivity does not alter disease outcome per se. This is in agreement with the findings of Albers et al. [18] who reported no difference in ANA status between patients with a remitting and an unremitting course 3–5 years after diagnosis. In contrast, Guzman et al. [15] found that ANA positivity was associated with increased risk of any flare after attaining inactive disease and this was only partly explained by their association with uveitis (Hazard ratio (HR) 1.16 when excluding all flares with uveitis). Notably, they define the cut-off for ANA positivity as low as 1:80 which can explain the higher ANA positivity (43.7%) compared to our cohort and may contribute to the high HR.

Compared to ANA-positive patients, Ravelli et al. [7, 8] found that the cumulative number of affected joints during the first 6–24 months of disease was higher in ANA-negative patients irrespective of being categorized as oligo- or polyarticular JIA. This made Ravelli et al. conclude that ANA-positive patients should be classified as a separate category [7, 8]. In contrast, our study reports no significant difference in joint counts in ANA-positive and ANA-negative patients; both at diagnosis and after more than 5 years on average at last follow-up. The latter remained present even with all JIA subcategories represented, while Ravelli et al. [7, 8] did not include all JIA subtypes, but excluded systemic, enthesitis-related, and RF-positive polyarticular JIA.

Further, remission rates on and off medication according to the Wallace preliminary criteria were not significantly different, but very comparable in ANA-positive and ANA-negative patients. This again would not support the hypothesis that ANA positivity alone should be a separate category.

There are some limitations to this study. This is a retrospective study and this design could potentially lead to bias. However, the population studied includes all patients seen in one single tertiary center in Denmark, with a relatively homogeneous ethnical Danish population. This is still the largest study completed to date evaluating outcome based on ANA positivity, and analysis provides a clear picture of the remission rates overall and in both groups. Notably, ANA testing was performed by indirect immunofluorescence (IIF) assays on HEp-2 cells [19, 20] since testing for ANA using an enzyme-linked immunosorbent assay (ELISA) has shown limited value in patients with JIA [21]. However, the IIF test has been criticized for its variability among studies [6] which may be explained by the use of the test among different ethnical groups also known for differences in distribution of JIA subcategories [22]. All ANA tests in this study were performed with at least 3 months’ interval, by the same method, and in the same lab during the years of investigation and as in previous studies [7, 8] the minimum cut-off titer for ANA positivity used here was set at 1:160 in order to lower the risk of false-positive results.

In conclusion, this study shows there is no difference in the number of active joint count at diagnosis and at follow-up or in remission rate based on ANA positivity in children with JIA. The ANA-positive patients are more frequently girls, have a younger onset age, and have associated uveitis, but these factors, however, do not differ their remission rates in this cohort. Our data do not support the hypothesis for a possible separate JIA category based on ANA positivity.