HSV encephalitis vs Bacterial meningitis
How to tell HSV encephalitis and Bacterial meningitis apart when a board question makes them look alike.
HSV encephalitis: fever with cortical signs and temporal lobe MRI changes; bacterial meningitis: fever with neck stiffness and neutrophilic CSF.
Side by side
Fever with early altered behavior, personality change, seizures, focal deficits, and possible temporal lobe involvement.
Fever, headache, neck stiffness, neutrophilic CSF, low glucose, and high protein.
HSV infects brain parenchyma, classically temporal lobes.
Bacteria infect meninges and drive neutrophilic meningeal inflammation.
CSF HSV PCR supports HSV encephalitis; temporal lobe abnormalities may appear but should not be the first clue.
Low CSF glucose with neutrophils supports bacterial meningitis.
The trap
Both share fever and headache, but cortical signs (personality change, aphasia, focal seizures, hemiparesis) shift the diagnosis to encephalitis. Start empiric acyclovir 10 mg/kg IV every 8 hours as soon as HSV is on the differential and do not wait for CSF PCR. Delayed acyclovir more than doubles mortality and worsens cognitive outcomes. In practice, broad empiric therapy covers both: acyclovir plus ceftriaxone plus vancomycin until CSF results return.
Watch it explained
Test it nowThe repair move
When altered behavior or seizures dominate, treat it as brain parenchyma involvement, not simple meningitis.
Try a free question
CoreA febrile patient develops personality change, confusion, and seizures. CSF PCR is positive for HSV. Which diagnosis is most likely?
Show answer and explanation
Answer: A. HSV encephalitis. Fever with altered behavior/seizures and HSV PCR positivity points to HSV encephalitis.
Why the other choices are tempting
- B. Bacterial meningitis centers on meningeal inflammation with neutrophilic low-glucose CSF.
- C. Viral meningitis has meningeal symptoms without prominent parenchymal dysfunction.
- D. Subarachnoid hemorrhage causes sudden severe headache and blood in CSF/CT.
- E. Brain tumor is usually subacute and noninfectious.
Flashcards
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What is the fastest separator for HSV encephalitis vs Bacterial meningitis?
HSV encephalitis: fever with cortical signs and temporal lobe MRI changes; bacterial meningitis: fever with neck stiffness and neutrophilic CSF.
What clue should make you choose HSV encephalitis?
Fever with early altered behavior, personality change, seizures, focal deficits, and possible temporal lobe involvement.
Quick answers
What is the fastest way to tell HSV encephalitis from Bacterial meningitis?
HSV encephalitis: fever with cortical signs and temporal lobe MRI changes; bacterial meningitis: fever with neck stiffness and neutrophilic CSF.
What is the key clue for HSV encephalitis?
Fever with early altered behavior, personality change, seizures, focal deficits, and possible temporal lobe involvement.
What is the key clue for Bacterial meningitis?
Fever, headache, neck stiffness, neutrophilic CSF, low glucose, and high protein.
What is the common trap with HSV encephalitis vs Bacterial meningitis?
Both share fever and headache, but cortical signs (personality change, aphasia, focal seizures, hemiparesis) shift the diagnosis to encephalitis. Start empiric acyclovir 10 mg/kg IV every 8 hours as soon as HSV is on the differential and do not wait for CSF PCR. Delayed acyclovir more than doubles mortality and worsens cognitive outcomes. In practice, broad empiric therapy covers both: acyclovir plus ceftriaxone plus vancomycin until CSF results return.