There have been numerous studies of initial IVIG resistance in KD, but few reports on repeated IVIG resistance [21–26]. In our retrospective investigation, the incidence of initial IVIG resistance was about 11.91% (112/940), and the rate of repeated IVIG resistance was about 4.25% (40/940). It has been reported that age less than 3 months, incomplete KD, incidence of CAA and initial administration of IVIG ≤ 4.0 days were associated with initial IVIG resistance [27–31]. The hypercoagulation of increased APTT, PT and D-dimer and the abnormal liver function of increased ALT, AST, TB were confirmed as the risk factors favor initial IVIG resistance [22, 32–35]. The raise of WBC, PLT, CRP, ESR, creatinine, blood urea nitrogen and the decline of Hb were also observed in KD children with initial IVIG resistance [35–38]. But, these clinical data and laboratory data were not associated with repeated IVIG resistance, since there were no differences between the repeated IVIG-responsive group and repeated IVIG-resistant group in our research. These differences have not been found in other studies either21–24.
However, we founded that KD children with repeated IVIG resistance had higher N%, PCT, and lower ALB, Na + compared with KD children responding to repeated IVIG treatment, which is also confirmed associating with both initial and repeated IVIG resistance in other studies [21–23, 39–43], indicating more serious inflammation and increased vascular permeability [35, 44, 45]. It suggested these children may require more aggressive anti-inflammatory therapy. Whether enhancing initial anti-inflammatory treatment could decrease the incidence of CAA remains controversial [18, 46–49]. The incidence of CAA during hospitalization was relatively higher in KD children with repeated IVIG resistance in our study, despite lacking statistical differences. Meanwhile, a significantly higher level of NT-proBNP, which is an important cardiac biomarker that associating with ventricular myocyte ischemia and hypoxia [50], was observed in these children, indicating that timely control of inflammation could reduce myocardial injury.
Predictive values of N%, Na+, ALB, PCT and NT-proBNP on repeated IVIG resistance in KD were further explored in our study, and found that PCT > 1.81ng/ml (OR = 4.161) on admission may be an independent predictor of repeated IVIG resistance in KD yielded sensitivity of 80.00% and specificity of 64.80%. NT-proBNP yielded the highest specificity of 85.19% in our study, which was reported to be a predictor of initial IVIG resistance [33, 36, 51, 52], but it failed to predict repeated IVIG resistance, the reason may be due to relatively low sensitivity of 45.00%. At its root, perhaps, the mechanism of IVIG resistance is an immune response that causes systemic vasculitis, not only damage to the coronary arterial wall [53]. Production and secretion of PCT is promoted by inflammatory cytokines such as tumor necrosis factor-α and interleukin-6 [54], which are also major inflammatory factors of KD [55]. Endothelial cell function could be impaired by PCT under an inflammatory state, which leading to loss of an endothelial barrier that may contribute to capillary leakage, hypercoagulation, anti-angiogenic properties and even inducing endothelial cell death in vitro [45, 56–57]. Compared with NT-proBNP, PCT may be a better indicator of KD pathology, which may explain part of the mechanism underlying repeated IVIG resistance.
This study has some limitations. First, the sample size of this study is small, further multicenter prospective studies are needed to confirm our findings. Second, the present study had strict inclusion and exclusion criteria, the findings in our study were only applicable to KD patients receiving standardized IVIG treatment. Third, because laboratory data before repeated IVIG treatment were scarce, we only investigated the laboratory data on admission. Further studies are needed to look into the laboratory data after the initial IVIG treatment.