Basic approach to viral encephalitis

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