Encephalitis is a pathologic state of brain parenchymal dysfunction leading to an altered state of consciousness or focal neurologic signs.
Serious, complex, and potentially fatal disorder with noninfectious and infectious causes.
Presents with acute onset of a febrile illness and altered mental status; typical features include headache, seizures, and focal neurologic signs.
Investigations should include blood cultures, neuroimaging (preferably magnetic resonance imaging), and cerebrospinal fluid analysis.
Acyclovir should be administered as soon as possible in all cases of suspected viral encephalitis.
Complications include seizures, hydrocephalus, and neurologic sequelae (e.g., behavioral disturbances, motor problems).
Encephalitis is defined as inflammation of the brain parenchyma associated with neurologic dysfunction, such as altered state of consciousness, seizures, personality changes, cranial nerve palsies, speech problems, and motor and sensory deficits. It is the result of direct inflammation of the brain tissue, as opposed to the inflammation of the meninges (meningitis), and can be the result of infectious or noninfectious causes. An etiologic agent is only identified in around 50% of cases.
History and exam
Key diagnostic factors
- altered mental state
- focal neurologic deficit
- optic neuritis
- acute flaccid paralysis
- movement disorder
Other diagnostic factors
- gastrointestinal infection
- biphasic illness
- autonomic and hypothalamic disturbances
- age <1 or >65 years
- blood/body fluid exposure
- organ transplantation
- animal or insect bites
- hunting/trekking in woods
- swimming or diving in warm freshwater or nasal/sinus irrigation
- spelunking (cave-exploring)
- death in animals
1st investigations to order
- peripheral blood smear
- serum electrolytes
- liver function tests
- blood cultures
- throat swab
- nasopharyngeal aspirate
- sputum culture
- chest radiography
- CT brain
- MRI brain
- electroencephalogram (EEG)
- cerebrospinal fluid (CSF) analysis
- CSF culture
- CSF serology
- CSF polymerase chain reaction (PCR)
Investigations to consider
- urine culture
- stool enteroviral culture
- IgG and IgM antibodies (blood)
- PCR (blood)
- HIV serology/RNA test
- CSF biomarkers/prion protein assay
- paraneoplastic antibodies (blood and CSF)
- abdominal/pelvic ultrasound
- whole-body CT
- whole-body PET scans
- magnetic resonance spectroscopy
- next-generation sequencing of CSF
- brain biopsy
immunocompetent host: suspected viral etiology
immunocompromised host: suspected viral etiology
confirmed herpes simplex virus (HSV) encephalitis
confirmed varicella zoster virus (VZV) encephalitis
confirmed cytomegalovirus (CMV) encephalitis
confirmed Epstein-Barr virus (EBV) encephalitis
confirmed herpes B encephalitis
confirmed human herpes 6 encephalitis
confirmed nonherpes virus etiology
convalescent phase: all etiologies
Payal B. Patel, MD
Department of Neurology
PBP declares that she has no competing interests.
Dr Payal B. Patel would like to gratefully acknowledge Dr Leo H. Wang, Dr Louise T. Wang, Dr Catalina C. Ionita, Dr Manjunath Markandaya, Dr David Janicke, Dr Robert Schmidt, and Dr Kimiko Domoto-Reilly, previous contributors to this topic.
LHW, LTW, CCI, MM, DJ, RS, and KDR declare that they have no competing interests.
Russel Dale, MBChB, MRCPCH, MSc, PhD
Professor of Paediatric Neurology
The University of Sydney
The Children's Hospital at Westmead
RD declares that he has no competing interests.
Arun Venkatesan, MD, PhD
Associate Professor, Neurology
Johns Hopkins Encephalitis Center
Johns Hopkins Hospital
AV declares that he has no competing interests.
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- EAN consensus review on prevention, diagnosis and management of tick‐borne encephalitis
- Case definitions, diagnostic algorithms, and priorities in encephalitis: consensus statement of the International Encephalitis Consortium
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