Etiologies-encephalitis

(specific etiology found in <20% of cases; Neurology 2006;66:75; CID 2008;47:303)

• HSV-1 all ages/seasons. If sxs recur after Rx, consider viral relapse vs. autoimmune encephalitis b/c high rates of autoimmune disease wks later (Lancet Neurol 2018;17:760).
• VZV 1° or reactivation; ± vesicular rash; all ages (favors elderly), all seasons
• Arboviruses: evaluate for exposure to vector/geography. Mosquitoes: West Nile, Eastern/Western equine, St. Louis, La Crosse; Ixodes tick: Powassan.
• Enteroviruses (coxsackie, echo): preceding URI/ GI sx; peaks in late summer/early fall
• Other infectious: CMV, EBV, HIV, JC, measles, mumps, rabies, adeno, influenza, Lyme
• Non-infectious: autoimmune/paraneoplastic (anti-NMDAR, anti-Hu, anti-Ma2, anti-CRMP5, anti-mGluR5), post-infxn demyelination (eg, ADEM)