Encephalitis

About Encephalitis

Encephalitis is inflammation of the brain parenchyma itself, as opposed to meningitis which affects the surrounding membranes. It is less common than meningitis but more severe, with significant mortality and morbidity. Causes include viral infections HSV, VZV, enteroviruses, arboviruses West Nile, Eastern Equine, Zika, autoimmune anti NMDA receptor, and post infectious acute disseminated encephalomyelitis ADEM. Herpes simplex encephalitis HSV 1 is the most common cause of sporadic viral encephalitis in the US, affecting the temporal lobes. Symptoms develop over hours to days and include fever, headache, confusion, personality changes, seizures, focal neurological deficits, speech difficulties, and decreased consciousness. Unlike meningitis, altered mental status is a defining feature. Diagnosis requires MRI showing brain inflammation, EEG showing characteristic abnormalities periodic lateralized epileptiform discharges in HSV, CSF analysis with PCR for viral pathogens, and autoimmune antibody testing. HSV encephalitis is treated urgently with intravenous acyclovir, which greatly reduces mortality compared with the roughly 70 percent seen without treatment. Autoimmune encephalitis requires immunotherapy steroids, IVIG, plasma exchange, rituximab. Post infectious encephalitis ADEM is usually self limiting but may respond to corticosteroids. In a large proportion of encephalitis cases no cause is identified. Sudden confusion, seizures, or reduced consciousness, especially with fever, is a medical emergency; call your local emergency number.