Encephalitis is an inflammation of the brain parenchyma, often caused by a viral infection or, less commonly, by a non-infectious inflammatory process.
Epidemiology:
Occurs worldwide with varying etiologies based on geographical regions.
Affects all ages, but incidence is higher in children, the elderly, and immunocompromised individuals.
Etiology:
Infectious Encephalitis:
Viral infections are the most common cause (e.g., herpes simplex virus (HSV), varicella-zoster virus, enteroviruses, arboviruses like West Nile virus).
Bacterial, fungal, and parasitic infections are less common.
Autoimmune Encephalitis:
Associated with immune-mediated processes.
Examples include anti-NMDA receptor encephalitis.
Pathophysiology:
Infection or autoimmune response leads to brain inflammation, neuronal damage, cerebral edema, and in severe cases, increased intracranial pressure.
Clinical Features:
Fever, headache, altered mental status (ranging from mild confusion to coma).
Seizures, focal neurological deficits, movement disorders.
Symptoms of meningitis (neck stiffness, photophobia) may also be present.
Diagnosis:
Lumbar puncture and CSF analysis: Elevated white cells, elevated protein, normal to low glucose.
PCR of CSF for viral pathogens.
EEG, MRI or CT scan to assess brain inflammation and exclude other causes.
Autoimmune encephalitis requires specific antibody testing.
Management:
Antiviral therapy (e.g., acyclovir for suspected HSV encephalitis) should be initiated promptly, often before the diagnosis is confirmed.
Supportive care: Management of seizures, intracranial pressure, hydration, and nutritional support.
Immunosuppressive therapy for autoimmune encephalitis.
Rehabilitation services for residual neurological deficits.
Prognosis:
Highly variable, depending on the etiology and promptness of treatment.
HSV encephalitis can be fatal if untreated, but treatment significantly reduces mortality and morbidity.
