Encephalitis is a pathological state of brain parenchymal dysfunction leading to an altered state of consciousness or focal neurological signs.
Serious, complex, and potentially fatal disorder with non-infectious and infectious causes.
Presents with acute onset of a febrile illness and altered mental status; typical features include headache, seizures, and focal neurological signs.
Investigations should include blood cultures, neuroimaging (preferably magnetic resonance imaging), and cerebrospinal fluid analysis.
Aciclovir should be administered as soon as possible in all cases of suspected viral encephalitis.
Complications include seizures, hydrocephalus, and neurological sequelae (e.g., behavioural disturbances, motor problems).
Encephalitis is defined as inflammation of the brain parenchyma associated with neurological 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 non-infectious causes. An aetiological agent is only identified in around 50% of cases.
History and exam
Key diagnostic factors
- presence of risk factors
- altered mental state
- focal neurological 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
- 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 aetiology
immunocompromised host: suspected viral aetiology
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 non-herpes virus aetiology
convalescent phase: all aetiologies
Payal B. Patel, MD
Assistant Professor of Neurology
Department of Neurology
University of Washington
PBP has received research funding support from the National Institute of Health and Bayer Pharmaceuticals. PBP has received an honorarium as an author from Medlink Neurology and Continuum Neurology.
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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