Objective To create an international consensus treatment recommendation for pediatric NMDA receptor antibody encephalitis (NMDARE). Methods After selection of a panel of 27 experts with representation from all continents, a 2-step Delphi method was adopted to develop consensus on relevant treatment regimens and statements, along with key definitions in pediatric NMDARE (disease severity, failure to improve, and relapse). Finally, an online face-to-face meeting was held to reach consensus (defined as ≥75% agreement). Results Corticosteroids are recommended in all children with NMDARE (pulsed IV preferred), with additional IV immunoglobulin or plasma exchange in severe patients. Prolonged first-line immunotherapy can be offered for up to 3–12 months (oral corticosteroids or monthly IV corticosteroids/immunoglobulin), dependent on disease severity. Second-line treatments are recommended for cases refractory to first-line therapies (rituximab preferred over cyclophosphamide) and should be considered about 2 weeks after first-line initiation. Further immunotherapies for refractory disease 1-3 months after second-line initiation include another second-line treatment (such as cyclophosphamide) and escalation to tocilizumab. Maintenance immune suppression beyond 6 months (such as rituximab redosing or mycophenolate mofetil) is generally not required, except for patients with a more severe course or prolonged impairments and hospitalization. For patients with relapsing disease, second-line and prolonged maintenance therapy should be considered. The treatment of NMDARE following herpes simplex encephalitis should be similar to idiopathic NMDARE. Broad guidance is provided for the total treatment duration (first line, second line, and maintenance), which is dictated by the severity and clinical course (i.e., median 3, 9 and 18 months in the best, average, and worst responders, respectively). Recommendations on the timing of oncologic searches are provided. Conclusion These international consensus recommendations for the management of pediatric NMDARE aim to standardize the treatment and provide practical guidance for clinicians, rather than absolute rules. A similar recommendation could be applicable to adult patients.

The NLRP3 inflammasome is a molecular complex that translates signals from pathogens and tissue damage into inflammatory responses, and plays crucial roles in numerous neurological diseases. Activation of the NLRP3 inflammasome leads to caspase‐1 dependent cleavage of pro‐IL‐1β to form mature IL‐1β. By acting on the P2X7 purinergic receptor, extracellular ATP is one of the major stimuli that activates the NLRP3 inflammasome. Although microglia express multiple purinergic receptors, their roles in inflammasome‐mediated inflammation are largely unknown. We studied the role of the P2Y12 receptor, a metabotropic P2Y receptor enriched in microglia, on inflammation in vitro. Inhibition of the microglial P2Y12 receptor by PSB0739 or siRNA knockdown suppressed IL‐1β release. P2Y12 receptor‐deficient microglia displayed markedly attenuated IL‐1β mRNA expression and release. P2Y12 receptor blockade also suppressed IL‐6 production. Both IL‐1β and IL‐6 responses were augmented by extracellular ADP or ADP‐βS and were abrogated by PSB0739. Mechanistically, ADP‐βS potentiated NF‐κB activation. In addition, ADP altered mitochondrial membrane potential in combination with ATP and increased the number of caspase‐1 positive cells through the P2Y12 receptor. These results elucidate a novel inflammatory mechanism by which extracellular ADP acts on the P2Y12 receptor to activate NF‐κB and the NLRP3 inflammasome to enhance microglial inflammation.

Aim: To develop standardized diagnostic criteria for ‘infection‐triggered encephalopathy syndrome (ITES)’ and five specific clinical syndromes of ITES.Method: The draft definitions were based on existing criteria, standardized, and discussed by a panel of international experts using nominal group technique over 18 months to achieve consensus. All criteria use the same format: (1) presence of infection/fever; (2) clinical features including encephalopathy; (3) neuroradiological features on magnetic resonance imaging; (4) exclusion of other causes.Results: We first highlighted differences between ITES and infectious and autoimmune encephalitis, which is the most important differential diagnosis. Consensus was achieved to define five specific ITESs: acute encephalopathy with biphasic seizures and late reduced diffusion; acute necrotizing encephalopathy; mild encephalopathy with a reversible splenial lesion; acute fulminant cerebral oedema; and acute shock with encephalopathy and multiorgan failure. Two further conditions that are currently classified as epilepsy syndromes but have similar features to ITES, namely febrile infection‐related epilepsy syndrome and hemiconvulsion–hemiplegia–epilepsy syndrome, are also discussed.Interpretation: The consensus definition is expected to improve awareness of this disease concept, provide diagnostic framework, and facilitate future international research and clinical trials.

Objective: Increasing reports suggest a role for immunological mechanisms in febrile infection‐related epilepsy syndrome (FIRES). The objective of this study was to elucidate the efficacy and safety of intrathecal dexamethasone therapy (IT‐DEX).Methods: We assessed six pediatric patients with FIRES who were administered add‐on IT‐DEX in the acute (n = 5) and chronic (n = 1) phases. We evaluated clinical courses and prognosis. We measured cytokines/chemokines in cerebrospinal fluid (CSF) from FIRES patients at several points, including pre‐ and post‐IT‐DEX, and compared them with control patients with chronic epilepsy (n = 12, for cytokines/chemokines) or with noninflammatory neurological disease (NIND, n = 13, for neopterin).Results: Anesthesia was weaned after a median of 5.5 days from IT‐DEX initiation (n = 6). There was a positive correlation between the duration from the disease onset to the introduction of IT‐DEX and the length of ICU stay and the duration of mechanical ventilation. No patient experienced severe adverse events. Seizure spreading and background activities on electroencephalography were improved after IT‐DEX in all patients. The levels of CXCL10, CXCL9, IFN‐γ, and neopterin at pre‐IT‐DEX were significantly elevated compared to levels in epilepsy controls, and CXCL10 and neopterin were significantly decreased post‐IT‐DEX, but were still higher compared to patients with chronic epilepsy. IL‐6, IL‐8, and IL‐1β were significantly elevated before IT‐DEX compared to epilepsy controls, though there was no significant decrease post‐treatment.Interpretation: IT‐DEX represents a therapeutic option for patients with FIRES that could shorten the duration of the critical stage of the disease. The effect of IT‐DEX on FIRES might include cytokine‐independent mechanisms.

Microglia, as well as other tissue-resident macrophages, arise from yolk sac progenitors. Thus, it is likely that the central nervous system environment is critical for the acquisition of a distinct microglial phenotype. Several microRNAs that are enriched in the brain play crucial roles in brain development and may also play a role in the differentiation of microglia. To track the differentiation of hematopoietic cells into microglia, lineage-negative bone marrow cells were co-cultured with astrocytes in the absence or presence of microRNAs or their inhibitors. Microglia-like cells were identified as small, round cells that were immunopositive for CD11b, Iba1, CX3CR1, and triggering receptor expressed on myeloid cells (TREM)-2. Five microRNAs (miR-101a, miR-139-3p, miR-214*, miR-218, and miR-1186) were identified as modifiers of the differentiation of bone marrow-derived microglia-like cells. Among them, miR-101a facilitated the differentiation of bone marrow cells into microglia-like cells most potently. Small, round cells expressing CD11b, Iba1, CX3CR1, and TREM-2 were predominant in cells treated by miR-101a. miR-101a was abundantly expressed in non-microglial brain cells. Transfection of miR-101a into microglia significantly increased the production of IL-6 in response to LPS. Finally, miR-101a downregulated the expression of MAPK phosphatase-1. miR-101a, which is enriched in the brain, promotes the differentiation of bone marrow cells into microglia-like cells.

Background and objectives: To clarify whether severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection cause acute encephalopathy in children and which are the most common syndromes that cause them and what are the outcomes.Methods: A nationwide web-based survey among all members of the Japanese Society of Child Neurology to identify pediatric patients aged < 18 years who developed acute encephalopathy in Japan between 1 January 2020 and 31 May 2022 associated with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection confirmed by polymerase chain reaction or antigen tests using pharyngeal swabs. Acute encephalopathy was defined as acute onset of impaired consciousness lasting > 24 h or an altered mental state; neurological symptoms arising within 2 weeks of onset of COVID-19 or multisystem inflammatory syndrome in children (MIS-C)/pediatric inflammatory multisystem syndrome (PIMS); evidence of SARS-CoV-2 infection; and reasonable exclusion of other diseases. Patients were divided into the known clinico-radiological acute encephalopathy syndrome group and unexplained or unclassifiable acute encephalopathy group. Outcomes were assessed by pediatric cerebral performance category (PCPC) score at hospital discharge.Results: Of the 3,802 society members, 217 representing institutions responded, and 39 patients with suspected acute encephalopathy were reported, of which 31 met inclusion criteria. Of these patients, 14 were diagnosed with known clinico-radiological acute encephalopathy syndromes, with acute encephalopathy with biphasic seizures and late reduced diffusion (five patients) being the most common. Five developed acute encephalopathy associated with MIS-C/PIMS. Among 31 patients, 9 (29.0%) had severe sequelae or died (PCPC ≥ 4). Two of three patients with encephalopathy with acute fulminant cerebral edema and two with hemorrhagic shock and encephalopathy syndrome died. The PCPC scores were higher in the known clinico-radiological acute encephalopathy syndrome group than in the unexplained or unclassifiable acute encephalopathy group (P < 0.01).Discussion: Acute encephalopathy related to SARS-CoV-2 infection was demonstrated to be more severe than that caused by other viruses in Japan. Acute encephalopathy syndromes characterized by specific neuroradiological findings was associated with poor clinical outcomes.