encephalitis

Encephalitis is inflammation of the brain tissue. It can be caused by infections, most often viral, or by autoimmune processes. It is distinct from meningitis, which primarily involves the membranes around the brain and spinal cord, though the two may occur together as meningoencephalitis.

Causes include viral infections such as herpes simplex virus type 1, enteroviruses, West Nile, Zika, varicella-zoster, measles, and mumps; bacterial or fungal infections; parasitic infections such as Toxoplasma; and autoimmune encephalitis in which antibodies target brain cells (for example anti-NMDA receptor antibodies). In some cases no clear cause is identified.

Symptoms vary and may begin with fever, headache, and confusion. As the condition progresses, patients may develop seizures, personality or behavioral changes, impaired consciousness, focal neurological deficits, or coma. Respiratory or systemic symptoms may accompany the illness.

Diagnosis relies on clinical suspicion supported by investigations. Lumbar puncture often shows inflammatory changes in the CSF, with elevated white cells and protein; glucose may be normal or low. Magnetic resonance imaging (MRI) and electroencephalography (EEG) aid evaluation. Laboratory tests include polymerase chain reaction (PCR) testing of CSF for viral genomes and serology, alongside routine blood tests and imaging.

Treatment focuses on the underlying cause and supportive care. Immediate antiviral therapy with acyclovir is used if herpes encephalitis is suspected; broad-spectrum antibiotics may be given if bacterial co-infection is possible. Autoimmune encephalitis is treated with immunotherapy such as corticosteroids, intravenous immunoglobulin, or plasmapheresis, and treatment of any associated tumor if present.

Outlook varies. Early recognition and appropriate treatment improve outcomes, but many survivors have lasting neurologic deficits. Prevention relies on vaccination for certain infections, vector control for arboviruses, and risk-reduction strategies for autoimmune conditions when applicable.