A 45-year-old man presents with fever, temporal lobe seizures, and CSF showing lymphocytic pleocytosis. HSV PCR on CSF drawn on day 1 of admission is negative, but clinical suspicion for herpes simplex encephalitis remains high. The most appropriate next step is:

• A Discontinue empiric acyclovir since PCR is definitive when negative
• B Repeat CSF HSV PCR in 48 to 72 hours while continuing acyclovir ✓
• C Send serum HSV IgG titers on the same day
• D Perform CSF viral culture and await results before treating

Explanation

CSF HSV PCR has a sensitivity of about 95 percent overall but is lower in the first few days of illness, so an early negative result does not exclude herpes simplex encephalitis. Guidelines recommend continuing empiric acyclovir and repeating the CSF PCR within about 72 hours if suspicion persists. Viral culture of CSF is far less sensitive than PCR for HSV and takes days, and serology cannot confirm CNS infection.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.