Meningitis vs Encephalitis
How to tell Meningitis and Encephalitis apart when a board question makes them look alike.
Step 2 CK pairs are in open beta while clinical review finishes. Spot an issue? Tell us.
Altered mental status with focal deficits or seizures points to encephalitis.
Side by side
Fever, headache, neck stiffness, and photophobia with relatively preserved consciousness suggest meningitis.
Altered mental status, focal neurologic deficits, or seizures with fever suggests encephalitis.
Inflammation of meninges causes meningeal irritation and elevated CSF inflammatory markers.
Inflammation of brain parenchyma causes cortical dysfunction, seizures, and focal deficits.
Bacterial meningitis often shows CSF neutrophilic pleocytosis above 1000/uL, glucose below 40 mg/dL or CSF to serum ratio below 0.4, and protein above 100 mg/dL.
HSV encephalitis often shows lymphocytic CSF pleocytosis, elevated protein, normal or mildly low glucose, and temporal-lobe abnormalities on MRI with positive HSV PCR.
The trap
Patients with fever and headache receive antibacterial coverage only while encephalitic features are overlooked. Missing early acyclovir in suspected HSV encephalitis increases morbidity.
The repair move
Next best step: start empiric IV acyclovir 10 mg/kg every 8 hours immediately when encephalitis is suspected, alongside empiric antibacterial meningitis coverage when bacterial disease is not excluded, then tailor therapy to CSF PCR and cultures.
Try a free question
CoreA 22-year-old man has fever, headache, neck stiffness, and photophobia but is fully oriented without focal deficits. What is the next best step in management?
Show answer and explanation
Answer: A. Start empiric meningitis-directed antibiotics promptly after cultures and indicated imaging precautions. Classic meningitis presentation requires urgent empiric antibacterial treatment and diagnostic workup.
Why the other choices are tempting
- B. Wrong. Acyclovir alone omits key bacterial coverage.
- C. Wrong. Potential bacterial meningitis is a medical emergency.
- D. Wrong. Treatment should not wait for final culture.
- E. Wrong. Severe meningeal signs require infectious evaluation.
Flashcards
Tap a card to flip it.
Which neurologic finding favors encephalitis over isolated meningitis?
Altered mental status with focal deficits or seizures.
What CSF glucose ratio is a high-yield bacterial meningitis threshold?
CSF to serum glucose ratio below 0.4.
Quick answers
What is the fastest way to tell Meningitis from Encephalitis?
Altered mental status with focal deficits or seizures points to encephalitis.
What is the key clue for Meningitis?
Fever, headache, neck stiffness, and photophobia with relatively preserved consciousness suggest meningitis.
What is the key clue for Encephalitis?
Altered mental status, focal neurologic deficits, or seizures with fever suggests encephalitis.
What is the common trap with Meningitis vs Encephalitis?
Patients with fever and headache receive antibacterial coverage only while encephalitic features are overlooked. Missing early acyclovir in suspected HSV encephalitis increases morbidity.