Viral Encephalitis

Inflammation of brain parenchyma from viral infection, with HSV-1 as the most common identifiable sporadic cause in immunocompetent adults.

Other causes include arboviruses (Japanese encephalitis, West Nile virus, tick-borne encephalitis, per regional epidemiology), enteroviruses, VZV, and, in the immunocompromised, CMV and HHV-6. A substantial proportion remain of unidentified cause despite thorough workup.

Fever, headache, altered consciousness, seizures, and focal neurological signs, with the specific pattern sometimes suggesting a cause (temporal lobe involvement favoring HSV; movement disorder or flaccid paralysis favoring certain arboviruses; cerebellar signs favoring VZV).

Distinguishing encephalitis from meningitis rests on the presence of altered brain function (confusion, seizures, focal deficit) beyond meningism alone.

CSF typically shows a lymphocytic pleocytosis with normal or mildly elevated protein and normal glucose.

PCR panels for HSV, VZV, enterovirus, and other regionally relevant pathogens; specific arbovirus serology (IgM) where endemic exposure is relevant.

MRI to assess pattern and severity, and EEG to characterize seizure activity and support diagnosis where PCR is negative but the syndrome is compatible.

• Empirical IV aciclovir 10 mg/kg every 8 hours started immediately in any suspected encephalitis pending PCR results, given HSV is the most treatable and most catastrophic-if-missed cause; stopped once HSV PCR (and, where relevant, a repeat sample at 3 to 7 days) is confirmed negative and an alternative diagnosis is more likely
• Supportive care: seizure control, management of raised intracranial pressure, ICU support for significant reduction in consciousness
• Most arboviral and enteroviral encephalitides have no specific antiviral treatment and are managed supportively
• CMV encephalitis (immunocompromised): ganciclovir or foscarnet, per specialist guidance

Referral: neurology and infectious disease for all cases; ICU for significant compromise.