This document discusses viral encephalitis, including: - Encephalitis is inflammation of the brain parenchyma that can cause altered mental status, motor/sensory deficits, and seizures. It is differentiated from meningitis which involves the meninges. - Viral encephalitis can be primary, caused by direct viral invasion of the brain, or postinfectious. Common viruses include HSV, VZV, influenza, and enteroviruses. - Clinical manifestations include fever, headache, vomiting, altered mental status, and focal neurological abnormalities. Investigations include imaging, EEG, and CSF analysis to identify the causative virus. Treatment involves supportive care and antivirals for certain

1. Viral
Encephalitis
BY
Dr Nauman Zafar
PGR Medicine

2. Introduction
 Encephalitis is Inflammation of brain
parenchyma
 Clinical manifestation include altered mental
status, motor or sensory deficits, speech or
movement disorders, seizures, hemiparesis,
flaccid paralysis, and paresthesias

3. Cont…..
 Contrast with meningitis which is inflammation
of meninges
 Meningitis is usually differentiated from
encephalitis with intact cerebral functions and
sign of meningeal irritation
 Both meningitis and encephalitis may co-exist
and term meningoencephalitis is used

4. Viral Encephalitis
 Can be primary or post infectious
 Primary infection:
 Characterized by viral invasion of the CNS
 Neuronal involvement can be identified on
histologic examination, electron microscopy,
or culture

5. Cont…..
 Postinfectious encephalitis :
 Also called acute disseminated
encephalomyelitis or ADEM
 A virus cannot be detected or recovered and
the neurons are spared
 Perivascular inflammation and demyelination
are prominent in this entity
 An immune-mediated disease
 MRI may demonstrate multifocal lesions
mainly involving supratentorial white matter

6. Responsible Viruses
 HSV-1,HSV-2
 VZV (herpesvirus)
 Influenza virus (orthomyxovirus)
 Enteroviruses (picornavirus)
 Rabies virus (rhabdovirus)
 Lymphocytic choriomeningitis virus (arenavirus)
 Lassa virus (arenavirus)
 Mumps virus (paramyxovirus)
 Measles virus (paramyxovirus)

7. Cont…..
 St Louis encephalitis virus (flavivirus)
 Japanese encephalitis virus (flavivirus)
 West Nile virus (flavivirus)
 Far East encephalitis virus (flavivirus)
 Central European encephalitis virus
(flavivirus)
 Dengue virus (flavivirus)
 La Crosse virus (bunyavirus)
 Colorado tick fever virus (orbivirus)

8. Clinical Manifestations
 Fever
 Headache
 Nausea and vomiting
 Altered mental status (subtle deficits to
complete unresponsiveness)
 Irritability and agitation
 Seizures

9. Cont…..
 Focal neurologic abnormalities (hemiparesis,
cranial nerve palsies, and exaggerated deep
tendon reflexes)
 Signs of meningeal irritation (photophobia and
nuchal rigidity) are usually absent with a pure
encephalitis but often accompany a
meningoencephalitis

10. Clues Regarding Etiology
 Parotitis (mumps encephalitis)
 Flaccid paralysis and maculopapular rash (West
Nile encephalitis)
 Tremors of the eyelids, tongue, lips, and
extremities (St. Louis encephalitis or West Nile
encephalitis)
 Hydrophobia, aerophobia, pharyngeal spasms,
and hyperactivity (encephalitic rabies)
 Grouped vesicles in a dermatomal pattern
(varicella-zoster virus)

11. Investigations
 Imaging studies
 EEG
 CSF Analysis
 Others

12. Imaging Studies
 MRI Brain is more sensitive than CT Brain in
detecting changes associated with
encephalitis
 CT Brain can rule out space occupying
lesions or hydrocephalus associated with non
viral etiologies

13. Cont…..
 Temporal lobe involvement (HSV, VZV, EBV,
human herpesvirus 6)
 Involvement of the thalamus or basal ganglia
(respiratory viral infection, arbovirus, West
Nile infection)

16. Electroencephalography (EEG)
 Often abnormal in acute encephalitis
 Focal abnormalities over the temporal lobes
(periodic spikes) may be observed in Herpes
Encephalitis

18. Cerebrospinal Fluid Findings
 Usually reveals
 Elevated proteins,
 Elevated WBCs(with lymphocyte
predominance)
 Normal glucose concentration
 Absent RBCs (non traumatic tap)

20. Cont…..
 CSF analysis has some drawbacks e.g.
 CSF analysis may be normal (e.g. 5-10%
cases of herpes encephalitis)
 Glucose may be slightly decreased (HSV,
mumps, some enteroviruses)
 RBCs may elevated (herpes encephalitis)
 Neutrophil predominance may be present (If
performed early)

21. Other tests
 Culture
 Polymerase chain reaction
 Serology

22. Differential Diagnosis
 Vasculitis
 Metabolic Encephalopathy
 Other infections
 Paraneoplastic and Autoimmune encephalitis
 Epilepsy
 Drugs and Toxins

23. Management
 Encephalitis is an acute, life-threatening
emergency, requiring prompt intervention
 Management includes
 Supportive Management
 Specific Management

24. Cont…..
 Supportive Management
 Airway Protection
 Ventilatory support if required
 Maintenance of circulation
 Fluid and electrolyte balance
 DVT prophylaxis
 Management of raised ICP
 Seizure control
 Nursing care

25. Cont…..
 Specific Management
 There are no specific therapies for most CNS
viral infections
 Empiric treatment for HSV-1 infection with
acyclovir 10 mg/kg IV Q8h (should always be
initiated as soon as possible if the patient has
encephalitis without apparent explanation)
 If HSE is diagnosed treatment is continued for
10-14 days

26. Prognosis
 Depends upon etiology
 Untreated herpes encephalitis has mortality
70% as compared to 20% if treatment is
started early
 Even in survivor there may be prominent
residual neurologic deficits