Encephalitis

Last reviewed: December 2018

Last updated: March 2018

Summary

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 MRI), and CSF 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).

Definition

Encephalitis is defined as inflammation of the brain parenchyma associated with neurological dysfunction [1] 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. Unfortunately, an aetiological agent is only identified in around 50% of cases. [1]

History and exam

Key diagnostic factors

presence of risk factors
fever
rash
altered mental state
focal neurological deficit
meningismus
parotitis
lymphadenopathy
optic neuritis
acute flaccid paralysis
movement disorder

Full details

Other diagnostic factors

cough
gastrointestinal infection
seizures
biphasic illness
autonomic and hypothalamic disturbances
myocarditis/pericarditis
jaundice
arthritis
retinitis
parkinsonism

Full details

Risk factors

age <1 or >65 years
immunodeficiency
vaccination
exposure to infected contacts
viral infections
blood/body fluid exposure
organ transplantation
animal or insect bites
location
season
occupation
hunting/trekking in woods
swimming or diving in warm freshwater or nasal/sinus irrigation
spelunking (cave-exploring)
death in animals
cancer

Full details

Diagnostic investigations

1st investigations to order

FBC
peripheral blood smear
serum electrolytes
liver function tests
blood cultures
throat swab
nasopharyngeal aspirate
sputum culture
chest radiography
CT brain
MRI brain
EEG
CSF analysis
CSF culture
CSF serology
CSF PCR

Full details

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)
whole-body CT
whole-body PET scans
magnetic resonance spectroscopy
next-generation sequencing of CSF
brain biopsy

Full details

Treatment algorithm

INITIAL

immunocompetent host: suspected viral aetiology

immunocompromised host: suspected viral aetiology

ACUTE

confirmed HSV encephalitis

confirmed VZV encephalitis

confirmed CMV encephalitis

confirmed EBV encephalitis

confirmed herpes B encephalitis

confirmed human herpes 6 encephalitis

confirmed non-herpes virus aetiology

non-viral aetiology

ONGOING

convalescent phase: all aetiologies

Contributors

Authors VIEW ALL 

Leo H. Wang, MD, PhD

Assistant Professor

Department of Neurology

University of Washington Medical Centre

Seattle

Disclosures

LHW declares that he has no competing interests.

Louise T. Wang, PharmD, BCPS

Clinical Pharmacist

Southern California Hospital

Culver City

Disclosures

LTW declares that she has no competing interests.

Robert Schmidt, MD, PhD

Professor, Pathology and Immunology

Head, Division of Neuropathology

Washington University School of Medicine

St. Louis

Disclosures

RS declares that he has no competing interests.

Kimiko Domoto-Reilly, MD

Assistant Professor

Department of Neurology

University of Washington

Seattle

Disclosures

KDR declares that she has no competing interests.

Acknowledgements

Dr Leo H. Wang, Dr Louise T. Wang, Dr Robert Schmidt, and Dr Kimiko Domoto-Reilly would like to gratefully acknowledge Dr Catalina C. Ionita, Dr Manjunath Markandaya, and Dr David Janicke, previous contributors to this monograph. CCI, MM, and DJ declare that they have no competing interests.

Peer reviewers VIEW ALL 

Russel Dale, MBChB, MRCPCH, MSc, PhD

Professor of Paediatric Neurology

The University of Sydney

Consultant Neurologist

The Children's Hospital at Westmead

Sydney

Australia

Disclosures

RD declares that he has no competing interests.

Arun Venkatesan, MD, PhD

Associate Professor, Neurology

Director

Johns Hopkins Encephalitis Center

Johns Hopkins Hospital

Baltimore

Disclosures

AV declares that he has no competing interests.

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