Encephalitis: Brain Inflammation — Symptoms, Causes, and Emergency Treatment

Encephalitis — inflammation of the brain parenchyma itself — must be distinguished from meningitis (inflammation of the brain's outer coverings). The distinction matters because encephalitis involves the brain tissue directly, producing neurological dysfunction — confusion, abnormal behaviour, seizures, focal deficits — in addition to fever. Encephalitis is rarer than meningitis but more dangerous, with significant mortality and morbidity even with treatment.

Causes

Viral encephalitis: The most common cause. Herpes simplex virus (HSV) encephalitis is the most important to recognise — it specifically targets the temporal lobes (producing personality change, memory disturbance, and temporal lobe seizures) and is treatable with IV acyclovir. Without treatment, HSV encephalitis has 70% mortality; with treatment, most patients survive. Other viruses: Japanese encephalitis (JE — a mosquito-borne flavivirus prevalent in rural India, vaccine-preventable); rabies (invariably fatal once symptomatic); enterovirus; EBV; CMV; dengue (rare neurological complication).

Autoimmune encephalitis: Increasingly recognised — the immune system attacks brain proteins. Anti-NMDA receptor encephalitis is the most common type (see separate article). Presents with psychiatric features, movement disorders, seizures, and autonomic instability. Responds to immunotherapy.

Post-infectious encephalitis (ADEM): Immune-mediated demyelination following viral infection or vaccination (see ADEM article).

Presentation

Fever + headache + altered consciousness or confusion — this triad should prompt immediate evaluation for CNS infection. Additional features: seizures (focal or generalised); personality change or bizarre behaviour; speech difficulty; focal neurological deficits.

Investigation and Treatment

Urgent CT brain (to exclude mass lesion before LP); lumbar puncture for CSF analysis and viral PCR; MRI brain with gadolinium (HSV encephalitis shows characteristic temporal lobe signal changes). Start IV acyclovir immediately if HSV encephalitis is suspected — do not wait for results. For fever with confusion: Sri Anand CNC, Chanda Nagar, Hyderabad. Call +91 90633 66983.