SARS-CoV-2 infection has caused a various range of serious neurologic complications including strokes, seizures, autoimmune diseases, and encephalopathies via several mechanisms comprising direct invasion, immune dysregulation, hypoxemia, thrombosis, multiorgan dysfunction, and cytokine storm . ANE, one of the serious encephalopathies of the brain, is believed to be caused by cytokine storm following viral infection rather than direct viral invasion itself . Other causes of ANE have been described in the literature; however, there has been limited solid evidence. Bacterial infection is an extremely rare cause of ANE. Only one case report described a patient who had Escherichia coli and Neisseria gonorrhoeae urinary tract infection and subsequently developed ANE . Another possible cause is vaccination; however, there are only few reports that ANE developed after recent vaccination. One case reported a previously healthy 6-month-old boy who was admitted to hospital with lethargy, hypotonia and focal clonic seizures 6 days following diphtheria, tetanus toxoid and whole-cell pertussis vaccination. ANE was diagnosed based on an exclusion of possible diseases accompanied with clinical and laboratory examinations, and imaging findings . Another case reported a 75-year-old Caucasian female who presented to the hospital with altered level of consciousness and dysarthria. She was diagnosed with ChAdOx1nCoV-1 vaccine associated ANE. She received her first dose of the ChAdOx1nCoV-1 vaccine 2 days prior to hospitalization and was also on a course of cephalexin for a presumed UTI. Testing of the patient’s serum for SARS-CoV-2 antibodies was negative . Apart from cytokine storm, gene mutation has also been reported to precipitate ANE .
As mentioned above, two main causes that induced ANE includes over production of cytokine and gene mutation. For cytokine production, IL-6 and TNF-alpha, at high levels can be neurotoxic and are the main cytokines causing proteolytic destruction of blood brain barrier. This process leads to both cytotoxic and vasogenic edema followed by petechial hemorrhages and necrosis . RANBP2 encodes a nuclear pore protein that mainly functions throughout the cell cycle, its mutations are strongly associated with ANE via multiple processes including mitochondrial function, viral entry, cytokine signaling, immune response, and blood–brain barrier maintenance . The RANBP2 mutation also causes cytokine storm, blood brain barrier disruption, impaired mitochondrial trafficking, and increased vulnerability to oxidative damage in setting of infection . A previous study in Japan showed that high serum IL-6 (> 15,000 pg/mL) is an indicator of a very poor prognosis in ANE in children (100% mortality) . Since the emergence of COVID-19, RANBP2 gene mutation has never been reported in COVID-19 cases. Therefore, this is the first case report. We believe that RANBP2 gene plays a crucial role in the propagation of ANE and might support the poor outcome and high IL-6 level in our patient. Furthermore, most of the COVID-19 related ANE patients from literature review  had severe pulmonary involvement, which needed intubation and invasive respiratory support; although, our case did not have pulmonary involvement, which is a unique case. We proposed that the extremely high IL-6 level might be responsible for the formation of ANE without the involvement of the respiratory symptoms. This has been reported in 6-year-old-boy of influenza virus associated ANE without pulmonary involvement in Thailand which resembles what we found in our case .
Hyper-responsiveness of the immune response and autoinflammatory phenomenon in patients with COVID-19 have been increasingly reported . IL-6 has been considered to be a promising marker of COVID-19 severity in which the level of IL-6 was found higher in severe cases compared with mild cases . Thus, it is believed to be deemed as a prognostic factor [13, 14] and a potential treatment target . However, the exact cut-off level of IL-6 regarding poor prognosis is unknown. One study found that mean level was only 21.55 pg/mL in severe COVID-19 (ranging from 1.5 to > 5000 pg/mL). From the study mentioned, it could be interpreted that the majority of patients did not have a high IL-6 level, despite the critical illness of the disease . However, it should be noted that acute elevated pro-inflammatory markers in COVID-19 are followed by immune suppression. In other words, the elevated level might be due to the timing of the blood collection . Although the IL-6 level in our case might be in the acute phase, the uniqueness of an extremely high IL-6 level could be precipitated from other unmentioned causes. Therefore, leading to a search for further contribution to this increased IL-6 level.
Vaccination is crucial for stopping the outbreak by raising humoral and cell-mediated immunity . However, antibody-dependent enhancement (ADE) exacerbating the severity of COVID-19 has been of great concern. The term ADE was first proposed in respiratory syncytial virus (RSV) and measles in which antibodies increase the severity of pathogens. The antibody-based vaccines including inactivated viral vaccines, which may contain non-neutralizing antigen targets and/or the S protein in non-neutralizing conformations, has a major concern of providing a non-protective target for antibodies that could increase the inflammation via ADE mechanisms like other respiratory pathogens such as RSV, Dengue virus, Zika virus, and Middle East Respiratory Syndrome Coronavirus . Two proposed mechanisms are enhancement of antibody-mediated virus uptake into Fc gamma receptor IIa (FcγRIIa) of the phagocytic cells and via the immune complex formation . In COVID-19, it is believed to involve both mechanisms. Antibodies that are responsible for the formation of immune complexes are non-neutralizing antibodies. They are antibodies that could bind to the virus but could not neutralized them. The concept of ADE mechanism of SARS-CoV-2 pseudoviral infection in vitro has recently proved that FcγRIIB-mediated uptake of SARS-CoV-2/mAb complex with bivalent. They reported that two neutralizing mAbs, MW01 and MW05, could enhance the infection of SARS-CoV-2 pseudovirus on FcγRIIB expressing B cells, which might lead to an increase in severity of viral infection . Therefore, forming a complement cascade. In conjunction with previous findings, it has been documented in RSV that non-neutralizing antibodies bind with viral antigens to initiate a complement cascade, secrete pro-inflammatory cytokines and recruit immune cells; later creating an over production of cytokine . Not all vaccines are reported to be responsible for the formation of immune complexes. Newer generations of vaccines (mRNA vaccines) that could produce S-specific neutralizing antibodies have a lower risk of ADE . On the contrary, inactivated vaccines elicit the non-neutralizing S protein which is hypothesized to possibly drive the production of inflammation .
The Brighton Collaboration Vaccine-associated Enhanced Disease Working Group has proposed the definition of the term “Vaccine Associated Enhanced Disease (VAED)” published in Vaccine, 2021 . Regarding the best available information in this case, the level of certainty of VAED could be a possible case of VAED (level 3B). We lack the immunopathology in target organs involved by histopathology such as presence of tissue eosinophils, elevated pro-inflammatory Th2 cytokine in tissue, complement activation, etc. Moreover, we differentiate vaccine failure, defined as the occurrence of the specific vaccine-preventable disease in a person who is appropriately and fully vaccinated, from VAED. In our case, the patient developed symptoms after 8 days after her 1st dose of an IVV, BBIBP-CorV; thus, the effective protective response for SARS-CoV2 infection might not have reached its maximum efficacy. According to the originally published phases 1 & 2 studies, more than 75% of vaccine recipients in the group aged 18–59 years seroconverted after the first vaccine dose (day 14) . The remaining vaccine recipients seroconverted on day 28 and 100% seroconversion was found in all participants on day 42. The second booster dose immunization raised the significantly greater neutralizing antibody titers than the days 0 and 14 schedule and the single immunization . Therefore, vaccine failure should also be taken into consideration in this case.
In regard to our patient’s clinical history, physical examination, laboratory diagnosis, genetic studies, and imaging studies, we could establish the diagnosis of ANE based on the proposed diagnostic criteria  by Mizuguchi et al.  and Neilson et al. . We believe that SARS-CoV2 infection, RANBP2 gene mutation, bacterial infection, and recent inactivated vaccination are separate events that interact with each other to cause over production of cytokines. Therefore, we hypothesized that all the above mentioned contributes to the formation of ANE in different degrees.
Further study is needed to confirm this hypothesis, specifically in the post-vaccination period. It is crucial that IVV should be carefully monitored and observed for safety concerns related to its possible complications. In addition, Role of RANBP2 mutation and its application in COVID-19 and ANE should be further elaborated.
We present an extremely rare case of ANE in COVID-19 with extremely high interleukin-6 and RANBP2 mutation despite the absence of significant pulmonary involvement. The combination of SARS-CoV2 infection and bacterial infection (culture proven) accompanying with predisposing genetic factor, RANBP2 gene mutation were the possible main causes of the illness. In addition, non-neutralizing antibodies caused by the 1st dose of IVV might play a possible role via ADE mechanism. Further study is needed to confirm this hypothesis, specifically in the post-vaccination period. We believe that multiple etiologies in our case precipitated the propagation of this condition and requires further attention for future studies.