142.1 🎓 醫孞生版

142.1.0.1 📌 䞀頁重點

  • Encephalitis = brain parenchyma inflammation + altered mental status, fever, seizure, focal neuro
  • Meningitis (meninges) vs encephalitis (brain) — clinical overlap (meningoencephalitis)
  • Etiology:
    • Viral (most common identifiable):
      • HSV-1 (#1 in adults sporadic, temporal lobe!) — treatable!
      • VZV, EBV, CMV, HHV-6, enterovirus, mumps, rabies
      • Arboviruses: WNV, JEV (Asia), EEE/WEE/SLE, Dengue, Powassan, Zika
      • HIV (acute or chronic)
    • Bacterial (rare cause of true encephalitis): Listeria, Bartonella, M. pneumoniae, syphilis
    • Fungal / Parasitic: Cryptococcus (HIV), Toxoplasma (HIV), free-living amoeba (Naegleria, Acanthamoeba)
    • Autoimmune: anti-NMDA receptor (paraneoplastic — ovarian teratoma), anti-LGI1, anti-CASPR2, anti-GAD, etc.
    • Post-infectious / ADEM: post-viral or post-vaccine
  • Empirical acyclovir 10 mg/kg IV q8h ASAP — don’t wait for results (HSV mortality 70% without Tx, 30% with)

142.1.0.2 1⃣ Diagnosis

142.1.0.2.1 Clinical
  • Fever (most), altered mental status (key!), seizure, focal neuro deficits, headache
  • Vs Meningitis: meningitis is meninges, encephalitis is brain parenchyma — meningoencephalitis 共存垞芋
142.1.0.2.2 Workup
  • LP ASAP (after CT if focal deficit / immunocompromised / papilledema)
  • CSF analysis:
    • Lymphocytic pleocytosis (10-1000), normal-mild ↑ protein, normal glucose
    • Hemorrhagic? → HSV-1 (RBCs 圚 CSF)
  • HSV PCR on CSF (sensitivity > 96%, do early!)
  • VZV, enterovirus, CMV, EBV PCR as indicated
  • Arboviral serology (WNV IgM in CSF)
  • MRI brain (better than CT) — HSV: temporal + frontal hemorrhagic lesion
  • EEG — frequent epileptiform discharges in HSV; subclinical seizures
  • Autoimmune workup (if no infection found): anti-NMDA, LGI1, CASPR2, GAD, paraneoplastic panel

142.1.0.3 2⃣ HSV Encephalitis (重點)

142.1.0.3.1 Clinical
  • 急性 (days) 癌燒、altered mental status、seizure (especially temporal lobe — déjà vu, smell, fear)
  • Mortality 70% untreated → 30% with Tx (15% morbidity-free)
142.1.0.3.2 Imaging
  • MRI: T2 / FLAIR hyperintensity in temporal lobe ± frontal; bilateral asymmetric (right > left common); hemorrhagic (gradient echo)
  • CT (insensitive early)
142.1.0.3.3 CSF
  • Lymphocytic pleocytosis (10-1000)
  • RBCs (50% — hemorrhagic encephalitis)
  • Protein ↑, glucose normal
  • HSV PCR (gold standard)
142.1.0.3.4 Treatment
  • Acyclovir 10 mg/kg IV q8h × 14-21 days (longer in immunocompromised)
  • Adjusted for renal function
  • Adverse: AKI (well hydrate!), thrombophlebitis

142.1.0.4 3⃣ Autoimmune Encephalitis

142.1.0.4.1 Anti-NMDA Receptor Encephalitis (most common autoimmune)
  • 倚幎茕女性 + ovarian teratoma (~ 50% paraneoplastic)
  • 男性 + 兒童 less paraneoplastic
  • Stages: prodrome (flu-like) → psychiatric (psychosis, agitation, mutism) → seizure / movement disorder → autonomic instability / coma
  • Antibody against NMDA receptor (NR1 subunit) in CSF
  • MRI 倚正垞 / subtle
  • Treatment:
    • Tumor removal if found
    • First-line: IV methylprednisolone + IVIG OR plasmapheresis
    • Second-line: rituximab + cyclophosphamide
  • ICU support — recovery 6-12 mo months
142.1.0.4.2 Other Autoimmune Encephalitides
  • Anti-LGI1: faciobrachial dystonic seizures, hyponatremia, older men
  • Anti-CASPR2: Morvan syndrome (insomnia, dysautonomia, neuromyotonia)
  • Anti-GAD65: stiff person syndrome, refractory epilepsy
  • Anti-Hu, anti-Yo, anti-Ma2, anti-CRMP5: paraneoplastic, classic onconeural Ab

142.1.0.5 4⃣ 其他 Viruses

142.1.0.5.1 West Nile Virus (WNV)
  • 矎國 / 加拿倧 summer; mosquito-borne
  • 倧倚 asymptomatic; 1% → neuroinvasive (encephalitis, meningitis, AFP-like paralysis)
  • Anterior horn cell (poliomyelitis-like) → asymmetric flaccid paralysis
  • Dx: WNV IgM in CSF
  • Tx: supportive
142.1.0.5.2 Japanese Encephalitis (JEV)
  • Asia; mosquito; rural rice paddies + pigs
  • Severe encephalitis: 30% mortality, 30-50% sequelae
  • JEV vaccine for travelers + endemic residents
  • Dx: serology IgM
  • Tx: supportive
142.1.0.5.3 Rabies
  • Bat, dog bite (Asia)
  • Encephalitic (“furious”) vs paralytic forms
  • Hydrophobia, aerophobia
  • Once symptomatic, mortality ~ 100% (only handful of survivors with Milwaukee protocol)
  • Post-exposure prophylaxis (PEP): RIG (rabies Ig) + vaccine × 4 doses before symptoms = 100% effective