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Background: From time to time, physicians face challenging diagnostic and therapeutic issues concerning the acute management of children with viral encephalitis., Objectives: The aim of this article is to provide an updated narrative review on the similarities and differences between SARS-CoV-2 and influenza encephalitis., Methods: A PubMed search was performed with the function "Clinical Queries" using the key terms "SARS-CoV-2" OR "Influenza" AND "Encephalitis". The search strategy included metaanalyses, clinical trials, randomized controlled trials, reviews and observational studies. The search was restricted to the English literature and pediatric population. This article compares similarities and contrasts between SARS-CoV-2 and influenza-associated encephalitis., Results: Encephalitis is an uncommon manifestation of both influenza and SARS-CoV-2. Both viruses are associated with fever and respiratory symptoms. However, SARS-CoV-2 patients may only have mild symptoms or be asymptomatic as silent carriers, rendering the disease spread difficult to control. Influenza patients usually have more severe symptomatology and are often bed bound for several days limiting its spread. Influenza is associated with seasonal and annual outbreaks, whereas SARS-CoV-2 has become endemic. Complications of encephalitis are rare in both viral infections but, when present, may carry serious morbidity and mortality. Many long-term sequelae of COVID- 19 infections (long COVID-19) have been described but not with influenza infections. Mortality associated with encephalitis appears higher with influenza than with SARS-CoV-2. Prophylaxis by immunization is available for both influenza and SARS-CoV-2. Specific efficacious antivirals are also available with oseltamivir for influenza and nirmatrelvir/ritonavir for SARS-CoV-2. Steroids are indicated with more severe SARS-CoV-2 but their role is not distinct in influenza disease., Conclusion: Encephalitis is a rare complication of influenza and SARS-CoV-2 infections. Both carry significant morbidity and mortality. Efficacious vaccines for prophylaxis and antivirals for treatment are available for both viruses., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.net.)

A 25-year-old female veterinarian presented with 1-week of flu-like symptoms followed by progressive encephalopathy. She was originally from Nicaragua and had been in the USA for 4 months. In the emergency department, she was confused and non-verbal with meningismus and facial myoclonus, but with an otherwise non-focal neurological exam. MRI brain abnormalities were consistent with viral encephalitides. Influenza B was detected via nasopharyngeal swab PCR. Mental status improved rapidly with oseltamivir. In such presentations, especially during flu season, influenza encephalitis must be considered, to facilitate early recognition of this entity and allow for targeted treatment.

Influenza encephalopathy, a rare manifestation of influenza infection in the adult population which is not widely recognised, can present with confusion and focal neurological symptoms, including aphasia. The aim of this report is to illustrate the unique presentation of influenza encephalopathy and discuss the need for close attention to and monitoring of this rare but highly fatal disease.A 28-year-old woman was admitted with acute-onset confusion and incoherent speech. CT of the head was unremarkable. Cerebrospinal fluid analysis showed elevation of protein, but was otherwise unremarkable. A detailed history revealed recent upper respiratory symptoms which prompted a rapid influenza test which was positive and oseltamivir was started. The patient's confusion and aphasia gradually improved and her speech was back to her baseline by the next day., Competing Interests: Competing interests: None declared., (© BMJ Publishing Group Limited 2020. No commercial re-use. See rights and permissions. Published by BMJ.)

Influenza-associated acute encephalopathy (IAE) is more prevalent in children than in adults and often results in neurological sequelae or even death. Diagnosis of IAE is difficult as clinical presentation varies significantly and the influenza virus is rarely detected in cerebrospinal fluid. Moreover, seizures in adults due to influenza infection are rare. Herein, we describe the case of an adult presenting with both acute encephalitis and seizures. A 38-year-old female was admitted to the emergency department with acute respiratory symptoms and fever, followed by quick progression to stupor within 24 h. A rapid antigen test was influenza A-positive, and polymerase chain reaction of nasal secretions confirmed the H3N2 subtype. Brain magnetic resonance imaging showed bilateral water restriction lesions at the thalamus and the cerebellum and an electroencephalogram showed frequent episodic generalized sharp-and-slow waves over the bilateral frontal region. Based on the neuroimaging and laboratory findings, we diagnosed the patient with adult influenza A (H3N2)-related encephalitis complicated by seizure. Treatment with oseltamivir and anticonvulsants led to complete neurologic recovery by day 14. This report describes two unusual neurological manifestations of influenza A, i.e., encephalitis and seizures, in an adult. We emphasize that, in adults presenting with acute viral encephalitis, clinicians should consider influenza infection as part of the differential diagnosis, and that typical neuroimaging in conjunction with laboratory detection of influenza virus and/or intrathecal antibody production suggestive of IAE, may help establish an accurate diagnosis., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Acute necrotizing encephalopathy (ANE) is a severe neurologic complication caused by influenza virus that has been infrequently reported in adult population. The diagnosis is made on epidemiological, clinical, and neuroimaging suspicion, but is rarely confirmed by microbiological findings in samples from the central nervous system (CNS), thus making it difficult to define the mechanism of pathogenesis of influenza-associated encephalitis/encephalopathies (IAE). We report a microbiologically documented case of ANE caused by influenza A/H3N2, in a previously healthy adult patient infected during a flu epidemic in Asturias (Spain). Direct viral invasion of the CNS was demonstrated with the isolation of the virus in a brain biopsy.

Background: The novel pandemic influenza A (H1N1) 2009 virus (influenza A(H1N1)pdm09) caused an epidemic of critical illness, with some patients developing fatal encephalopathy as well as pneumonia., Methods: To investigate the actual efficacy of treatments, we investigated data from questionnaires regarding 207 cases that occurred between September 2009 and February 2010., Results: The outcomes were recorded in 188 of the 207 cases; 16 of 188 patients died, while 23 had sequelae. Anti-influenza drugs in patients with severe coma (Glasgow coma scale score of ≤ 8) were statistically effective. In 165 out of 199 cases, steroid pulse treatment with methylprednisolone was given at an early stage. Other intensive treatments were mostly administered in serious cases., Conclusions: Controlled studies are needed to investigate the efficacy of other treatments except for anti-influenza drugs.

A 73-year-old man was admitted to our hospital with a high fever and left paresis. A rapid diagnosis test was positive for influenza A was positive by rapid diagnosis test and diffusion-weighted MRI imaging of the brain showed a high intensity lesion of the right cerebral peduncle. The patient was therefore diagnosed as having influenza A virus infection complicated with lacunar infarction. In spite of initial treatment with oseltamivir and anticoagulant therapy, he lost consciousness eight hours after admission. The high intensity lesion of the cerebral peduncle enlarged and new lesions in the thalamus, hippocampus and calcarine cortex were detected with brain MRI. Additionally, an electroencephalographic study showed an entire slow wave and as the other causative pathogens of central nerve system infection were not detected, the likely diagnosis was influenza-associated encephalitis. We administered a high dose of intravenous immunoglobulin since the low-grade fever and mild unconscious state had continued in spite of the treatment with methylprednisolone pulse therapy. His consciousness was restored and body temperature became normal immediately. We could confirm the efficacy of our treatment by measurement of IL-6 levels in the serum and cerebrospinal fluid during the entire clinical course. In conclusion, a high dose of intravenous immunoglobulin therapy might be one of the effective treatments for influenza-associated encephalitis.

We report an unusual case of pandemic (H1N1) 2009-related encephalitis in an immunocompetent woman. Although rare cases of pandemic (H1N1) 2009 associated with encephalitis have been reported previously, in this patient, direct viral invasion of the central nervous system was shown by simultaneous detection of viral RNA and pleocytosis.

Severe neurologic complications have been rarely reported during novel pandemic influenza A(H1N1) virus infections. We describe the case of an 10-year-old boy with new onset seizures and proven influenza A(H1N1) 2009 infection showing a reversible hyperintense lesion in the splenium of the corpus callosum on T2-weighted and FLAIR magnetic resonance images without contrast enhancement. Transient splenial lesions have been described in the context of virus encephalopathy and do not require specific treatment.

A 26-year-old man was admitted to our hospital because of high fever, drowsiness, memory disturbance, and disorientation due to H1N1 influenza virus-associated encephalitis/encephalopathy. All of his symptoms rapidly improved following methylprednisolone pulse therapy. The diffusion-weighted image of brain magnetic resonance imaging (MRI) revealed a large transient hyperintense signal lesion on the central splenium of the corpus callosum. This MRI finding in conjunction with a complete clinical recovery has been previously observed in cases of clinically mild seasonal influenza-associated encephalitis/encephalopathy, and can be also a useful clue for the diagnosis of new type of influenza, H1N1 influenza virus infection complicated by encephalitis/encephalopathy.

Encephalitis has been described as a rare complication of pandemic 2009 (H1N1) influenza A infection in children and adolescents. This report is on two adult patients who presented with encephalitis in relation to acute H1N1 influenza. Encephalitis is therefore also a potential complication of pandemic 2009 (H1N1) influenza infection in adults.

Seasonal influenza virus infection has been associated with a variety of neurologic complications. We report a case of novel influenza A (H1N1) encephalitis in an infant aged 3 months with an upper respiratory infection, who presented seizures. The infection was confirmed in nasopharyngeal aspirate and cerebrospinal fluid. Treatment with oseltamivir was started. He was discharged without any neurologic sequelae.

We describe a rare case of Influenza B-associated encephalopathy with hemorrhagic lesions of the corpus callosum. A 12-year-old Caucasian girl presented a 24-h fever followed by partial seizure, secondarily generalized, and disturbance of consciousness. Magnetic resonance imaging on Day 2 of her illness showed two hemorrhagic lesions of the corpus callosum. The Influenza B virus was found on nasopharyngeal swab. Neurologic signs had completely recovered by Day 3. A review of the literature identified a few similar cases; the common features include a relatively older age and prompt and complete recovery from clinical symptoms. This is the first report to describe hemorrhagic lesions of the corpus callosum in influenza., (Copyright 2010 Elsevier Masson SAS. All rights reserved.)

Cytochrome c and tumor necrosis factor-alpha concentrations were measured in serum and cerebrospinal fluid samples from 10 patients with influenza-associated encephalopathy. In the acute exacerbation phase, serum tumor necrosis factor-alpha and cytochrome c values were high in patients with a poor prognosis. In the convalescent phase, cerebrospinal fluid cytochrome c values increased remarkably in patients with subsequent brain atrophy.

The use of amantadine has been advocated as treatment for influenza A encephalitis despite limited information regarding cerebrospinal fluid concentrations and the pathogenesis of encephalitis associated with influenza virus infections. We report a 2-year-old child with influenza A encephalitis treated with amantadine who achieved a potentially therapeutic concentration in cerebrospinal fluid. Despite this the child developed significant neurologic impairment.

Encephalitis associated with acute influenza infection is unusual in nonepidemic years. A case of a 10-year-old child with influenza B encephalitis and profound weakness who was treated with oseltamivir is presented. This case illustrates several of the unusual findings associated with influenza infections and the result of treatment of influenza B encephalitis with oseltamivir.