Snapshot A 42-year-old male presentswith confusion, headache, and fever. The patient is unable to answer questions. A head CT is negative for a space-occupying lesion or hemorrhage. An MRI is shown. A lumbar puncture is performed, with cerebral spinal fluid (CSF) analysis showing a lymphocytic pleocytosis and normal glucose. PCR of the CSF is positive for HSV-1. Introduction Brain parenchymal infection abnormalities in brain functioning are expected e.g., altered mental status, changes in personality, problems with speech and movement this distinguishes encephalitis from meningitis Typically caused by infection viral (most cases) herpes simplex virus (HSV) most common cause varicella virus (VZV) epstein-barr virus (EBV) measles, mumps, rubella HIV Japanese encephalitis virus St. Louis encephalitis virus West Nile virus bacterial toxoplasmosis noninfectious acute disseminated encephalitis There can be both an infection of the brain parenchyma and meninges leading to a meningoencephalitis Presentation Symptoms seizues fever headache nausea vomiting Physical exam altered mental status personality changes focal neurological deficits cranial nerve palsies hemiparesis. meningsmus only in pure encephalitis Evaluation CT scan of the head MRI is the preferred imaging modality for HSV encephalitis Lumbar puncture perform after head imaging PCR most accurate for herpes encephalitis Brain biopsy last resort only if etiology is unknown Differential Intracranial malignancy primary or metastatic Medication side-effects Paraneoplastic or autoimmune disease anti-NMDA receptor encephalitis Treatment Treatment is dependent on etiology HSV encephalitis initiate acyclovir immediately can be considered with VZV encephalitis associated with a reduction in morbidity and mortality foscarnet in acyclovir-resistant herpes Prevention, Prognosis, and Complications 50 - 75% mortality in untreated HSV encephalitis < 1 or > 55 years old and immunocompromised is associated with poorer outcome