Time course of serum cytokine level changes within 72 h after onset in children with acute encephalopathy and febrile seizures

In most cases, children with seizures and/or impaired consciousness accompanied by fever with unknown etiology (SICF) are diagnosed with febrile seizures (FS) or acute encephalopathy (AE) [1]. Both of FS and AE are mostly associated with common infectious diseases such as influenza and exanthem subitem; there is a syndrome classification in AE such as acute necrotizing encephalopathy, acute encephalopathy with early biphasic seizures and later reduced diffusion (AESD), hemorrhagic shock and encephalopathy syndrome (HSES), and Reye-like syndrome [2, 3]. FS is a transient condition in which children do not experience sequelae, whereas AE is defined as impaired consciousness lasting longer than 24 h and is often associated with neurological sequelae [2]. Previous studies have indicated that the mortality rate among patients with AE is 6%, and many survivors exhibit motor and intellectual disabilities or epilepsy [2, 4]. Although FS and AE differ greatly in severity and outcomes, it is often difficult to distinguish AE from FS during the early stages of these diseases [2]. It has also been reported that some cases of AE progresses into a fatal condition within a few hours of onset [5], and also that early interventions may be effective in treating patients with AE [6, 7]. Therefore, it is necessary to identify a biomarker for distinguishing AE from FS within a few hours of onset.

The release of inflammatory cytokines is one of the major mechanisms involved in AE, hence, the anti-inflammatory treatment has been suggested [2]. There have been some previous reports on the use of cytokines as biomarkers for distinguishing AE from FS; however, their results were inconsistent [8‐11]. The drawback with previous reports on cytokines in SICF was that the cytokine dynamics might not have been fully captured. A recent study involving an animal model for febrile status epilepticus reported an increase in hippocampal interleukin (IL)-1β levels 1–3 h after febrile status epilepticus onset with rapid decline over 24 h and return to baseline by 96 h; IL-6 levels peaked later at 24 h [12]. Consequently, the timing of sample acquisition is important in the case of febrile status epilepticus, as cytokine levels change over time [13]. However, data on cytokines reported in previous studies on AE and FS were limited owing to daytime sampling units (only one sample per day) [9, 11, 14‐16].

Therefore, the purpose of this study was to explore the time course of serum cytokine level changes within 72 h after onset in SICF. Our hypothesis is that the levels of various serum cytokines would peak within 24 h after onset and that the levels of some cytokines would remain high after 24 h after onset.

This study showed that cytokine levels changed dynamically during the early stage of SICF, including AE and FS, within 72 h after onset. The levels of most cytokines were elevated immediately after onset, and those of several cytokines (IL-1β, IL-4, IL-6, IL-8, IL-17, eotaxin, FGF, IFN-γ, and MCP-1), including pro-inflammatory cytokines, peaked within 12 h after onset and decreased to around the control levels within 48 h after onset. Conversely, the levels of some cytokines, such as IL-1RA and IL-10, which are considered anti-inflammatory cytokines, did not decrease within 24 h after onset. This was not different from the findings of a previous report indicating that IL-10 and IL-1RA levels increased in FS [24].

In the present study, we made the final diagnosis according to the diagnostic criteria of Guidelines for the diagnosis and treatment of acute encephalopathy in childhood [2], and found that cytokine levels were elevated not only in AE but also in FS. A previous study reported that cytokine levels were elevated in FS [25, 26]. Regarding AE, inflammatory cytokines are thought to play an important role in severe AEs, such as HSES and acute necrotizing encephalopathy [2]. In contrast, the main mechanisms underlying AESD have been considered excitotoxic [2]. Reports have revealed that the levels of several cytokines are not elevated or are slightly elevated in AESD [8, 14, 15]. In the present study, the levels of some cytokines were elevated in AESD and FS and were as high as those in HSES. This result differs from that of previous reports. The reason for the elevated cytokine levels in AESD or FS might be because they were measured during the earlier stages than those in previous studies. Alternatively, pathogenic differences are a possible cause of elevated cytokine levels in AESD or FS because AE in children is generally thought to develop during the course of infectious diseases. In addition, cytokine levels were reported to be higher in HSES than in AESD [14, 15]; however, it was suggested that cytokine levels change dynamically over time, so they should be measured and compared regularly when used for diagnosis. The results of this study did not allow us to distinguish between AE and FS suggesting that AE and FS are overlapping syndromes representing a neuroinflammatory disorders triggered by fever mainly associated infections. Pensato et al. claimed that many febrile infection-associated encephalopathies including AESD, HSES and other syndromes showing overlapping clinical-radiological features and, presumably, similar pathogenesis. They said that those febrile infection-associated encephalopathies shared the same pathogenic mechanism of cytokine-mediated neuroinflammatory process, but to date, those above encephalopathies have been defined based on clinical presentation associated with specific investigative findings, irrespective of the pathogenic mechanisms [27]. Although FS was not mentioned in the study, it is possible that FS is also included in the spectrum of these encephalopathy disorders, as FS is triggered by febrile infection.

In clinical practice, the detailed time course of cytokine level changes in AE will aid in making clinical decisions regarding the administration of anti-inflammatory therapy. Based on our observations, it might be better to start anti-inflammatory treatment, such as steroid administration, within 12 h after onset because pro-inflammatory cytokine levels increase within 12–24 h after onset. The present study could not investigate whether HDS, TTM, or ECMO were effective in treating SICF because the disease severity and received therapies were different in each patient. Cytokine levels did not necessarily decrease within a few hours after the intervention with HDS or TTM. Moreover, some cytokine levels were high even after 12 h after onset; therefore, we suppose that anti-inflammatory treatments need to be continued after 12 h after onset. Though monoclonal antibody therapy for specific cytokine was not administered in patients in this study, it may be useful for patients whose cytokine levels are elevated. In future studies, we plan to compare cases with and without the administration of interventions.

This study has some limitations. Specimens were obtained by random blood sampling, and the sampling time was predetermined. The sample size was too small to show the exact dynamics of cytokines in different time point. Therefore, there is a need to perform the investigation in a larger number of patients. Because of the bias associated with anti-inflammatory treatment, the dynamics of natural cytokine levels are unknown and may have been modified. We also did not compare cytokine levels of AE and FS in this study, so the comparative study with a large number of cases is necessary in the future.

Cytokine levels in both AE and FS change dynamically from minutes to hours, such as the levels of several cytokines upstream of inflammation increased within a few hours after onset and decreased at 12–24 h after onset. Detailed knowledge of the time course of cytokine level changes will aid in making clinical decisions regarding the administration of anti-inflammatory therapy in 24 h after onset in AE. Although our study could not differentiate AE and FS by cytokine levels, but the results suggested that AE and FS may be neuroinflammatory spectrum disorders associated with fever because cytokine levels increased in all syndromes.