inpatient / infectious disease

Meningitis and Encephalitis

Last Updated: 1/21/2023

# Meningitis/Encephalitis

-- ABCs: 
is the patient protecting their airway?
-- Chart Check: h/o CNS tumor, other causes of increased ICP; previous head CT
-- HPI Intake: fever, malaise, nichal rigidity, headache; exposures
-- Can't Miss: bacterial meningitis, increased ICP
-- Admission Orders: CBC, BCx, coags, CT head if plan to get LP before starting abx if immunocompromised, CNS mass, seizure, AMS, focal deficit
-- Initial Treatment to Consider: do not delay antibiotics for an LP - if concerned, start empiric vanc, CTX, ampicillin (>50yo)

-- History: *** fever, malaise, nuchal rigidity, AMS, headache, college dorm, military exposures, tick exposures
-- Clinical/Exam: *** Kernig, Brudzinski’s, focal deficits, photophobia, seizure, rash/purpura
-- Data: *** BCx, CT Head, LP
-- Etiology/DDx: *** Meningitis - bacterial (S Pneumo, N meningitidis, H Flu, GBS, listeria); aseptic (enterovirus, HSV, VZV, syphilis, lyme, TB, HIV, fungal - cryptococcus, endemic myoses, candida, aspergillus), abscess, autoimmune (sarcoid, SLE), neoplastic (leukemia, lymphoma), drugs (Abx, NSAIDs); Encephalitis (viral, autoimmune, paraneoplastic)

The patient's HPI is notable for ***. Exam showed ***. Labwork and data were notable for ***. Taken together, the patient's presentation is most concerning for ***, with a differential including ***.

-- CT head if immunocompromised, CNS mass, seizure, AMS, focal deficit 
-- f/u LP studies (cell counts, glucose, protein, GS, cultures) and BCx
-- Encephalitis workup: CSF studies - HSV, VZV, West Nile, JC; MRI; EEG

-- Abx: *** Vanc and CTX; add ampicillin if >50yo; add cefepime and consider fungal coverage with amphotericin if immunocompromised
-- Acyclovir 10mg/kg q8 if c/f encephalitis
-- Dexamethasone if bacterial and GCS 8-11

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If You Remember Nothing Else

Meningitis is a CNS infection of the meninges whereas encephalitis is more global inflammation of the brain tissue. Meningitis is most commonly bacterial or viral, but can be caused by fungi, parasites, and other non-infectious etiologies. Bacterial meningitis can be life-threatening due to buildup of purulence in a limited intracranial space leading to increased pressure. The classic clinical triad for meningitis is fever, headache, and neck stiffness.

A lumbar puncture (LP) is the best way to diagnose meningitis or encephalitis, but should not be performed if there is increased ICP. Prioritize CT head before LP if the patient is immunocompromised, has a CNS mass, h/o seizures, is altered, or has a focal neurologial deficit on exam. If an LP must be delayed and there is high suspicion for bacterial meningitis, antibiotics should not be delayed. Empiric antibiotics for meningitis are vancomycin, ceftriaxone, and ampicillin (if >50 years old). If there is confirmed bacterial infection, add dexamethasone to reduce swelling.

Clinical Pearls

  • Classic triad of meningitis is fever, headache, neck stiffness
  • Vanc covers PCN-resistant strep pneumo and MRSA, CTX covers Neisseria and H flu, ampicillin covers listeria
  • Dosing of abx in the treatment of meningitis is often higher to improve blood-brain-barrier penetration (especially beta-lactams) 
  • Aseptic meningitis is most commonly caused by viruses (enterovirus, HSV, VZV), autoimmune, neoplasm, drugs
  • Fungal causes of meningitis include cryptococcus, endemic, candida, aspergillus
  • Encephalitis usually presents as AMS with focal deficits or seizure - HSV, VZV, West Nile, HIV, JC, anti-NMDA ab; treat with acyclovir and supportive care
  • MRI for encephalitis - HSV with temporal lobe enhancement, West Nile with basal ganglia focus
  • Waterhouse-Friderichsen syndrome is a complication of bacterial meningitis that leads to DIC and hemorrhage into the adrenal gland causing insufficiency

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