Viral encephalitis

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 B oth meningitis and encephalitis may co-exist and term meningoencephalitis is used

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

5. Cont ….. Postinfectious encephalitis : A lso 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)

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

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

16. 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)

17. Other tests Culture Polymerase chain reaction Serology

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

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

20. 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

21. 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

22. 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