In this study, we report significant differences in NFC parameters between children with noninfectious uveitis and pediatric controls, suggesting involvement of the systemic microcirculation in pediatric uveitis. Our results also suggest that the systemic microcirculation is affected even in idiopathic cases of uveitis that present without an identified systemic condition. Previous studies have shown that several inflammatory indicators such as the neutrophil/lymphocyte ratio, interleukins, and the platelet/lymphocyte ratio are elevated in the serum of patients with noninfectious uveitis [29–40]. These increased indicators are associated with both the activity and the severity of uveitis, likely implying activation of the systemic immune system (i.e., an inflammatory index). Our results support the notion that uveitis is not exclusively an intraocular inflammation but can also indicate systemic involvement. Although the long-term consequences of these changes in the microcirculation are currently unknown, our findings underscore the complexity of this potentially sight-threatening condition in children and provides new insights for developing diagnostic and prognostic biomarkers to monitor the microcirculation.
A previous cross-sectional case-control study in adults with uveitis found differences in NFC assessment, with a higher number of dilated capillaries and lower capillary density in the patient group [18]. Although we found no difference in capillary density between our entire pediatric uveitis group and the control group, we did find a significantly lower capillary density in the patients with anterior uveitis. This difference between studies might be due—at least in part—to differences between adult patients and pediatric patients and/or the slightly higher percentage of anterior uveitis patients in the previous study in adults (54%)[18] compared to our study (46%).
Recently, Melsens et al. reported that healthy children have a similar capillary density as adults and that the same cut-off value used for adults (≥ 7 capillaries per linear mm) can also be used in children [14]. Although not statistically significant, we found that 42% of the children with uveitis in our study had a capillary density < 7/mm compared to 20% of pediatric controls; this difference may be attributed in part to the fact that nearly half of the patients in our study had anterior uveitis, as anterior uveitis is often accompanied by a systemic disease such as JIA. However, the presence of JIA cannot fully explain this finding, as we found no difference between JIA-associated uveitis and idiopathic chronic anterior uveitis (data not shown). In addition, these two subtypes of uveitis are considered to be clinically identical, as they share genetic risk alleles and cannot be distinguished based solely on ophthalmological features [41, 42]. Moreover, recent studies in children with JIA found no changes in NFC parameters between patients with JIA (but for whom the presence of uveitis was unknown) and controls, indicating that arthritis might not be the cause of the changes in the microcirculation [14, 43].
Interestingly, we found that the patients with intermediate uveitis had the highest number of dilated capillaries per mm. Intermediate uveitis is often accompanied by signs of inflammatory involvement of the retina such as intraocular perivasculitis, vasculitis, and periphlebitis. In contrast to other studies in adults [18, 44], we found no apparent correlation between abnormalities in the retinal and nailfold microcirculation.
One strength of our study is that we included a relatively large cohort of children with uveitis. Furthermore, we assessed the NFC images using a standardized protocol based on the international consensus definitions established by the EULAR Study Group on Microcirculation in Rheumatic Diseases [12, 23]; these definitions were used recently in a standardized assessment of children [14]. In addition, the majority of the images was assessed by two observers who were blinded with respect to the participant’s details.
Despite these strengths, our study also has some limitations that warrant discussion. First, the pediatric control group was not age-matched to the patient group, resulting in a significant difference in age between the two groups; however, we corrected for both age and sex in of our analyses. Second, our prospective study did not show any apparent change in NFC findings, even after one year; however, this may have been too short of a follow-up period to detect changes, as a previous study involving patients with systemic sclerosis found that the median time to progression of the NFC pattern (i.e., the time after which 50% of patients did progress) was nearly four times as long as our follow-up period [45]. Longitudinal studies with repeated NFC measurements for a longer follow-up period are therefore needed in order to determine whether NFC findings have prognostic value with respect to predicting the course of disease severity in noninfectious uveitis. Furthermore, it would be interesting to investigate whether NFC findings can be used to predict disease relapse, the need for additional systemic treatment, and/or treatment response in patients with pediatric uveitis. On the other hand, future studies investigating the underlying pathophysiology are also needed in order to identify biomarkers specific to uveitis-associated inflammation and/or neoangeogenesis. Such studies will likely provide valuable information regarding the underlying disease mechanisms and may provide simple prognostic indicators that can be used to guide the precision care of patients with noninfectious uveitis.