Herpes simplex encephalitis (HSE) in adults most commonly results from reactivation of latent HSV-1 from the trigeminal ganglion with spread to the temporal lobe. The BEST initial diagnostic test for HSE when CSF is obtained is:
- A CSF HSV IgM antibodies (intrathecal production)
- B CSF India ink preparation for cryptococcal meningitis exclusion
- C CSF PCR for HSV-1/2 DNA ✓
- D Brain MRI with gadolinium — HSE-specific signal changes confirm diagnosis before CSF analysis
Explanation
CSF PCR for HSV DNA is the gold standard for diagnosing herpes simplex encephalitis — sensitivity 96–98%, specificity 99%. It replaced brain biopsy as the definitive test. CSF HSV IgM may not appear until 10–14 days after onset (too late for acute diagnosis), and intrathecal IgM detection is less sensitive. MRI showing temporal lobe signal changes (T2/FLAIR hyperintensity in medial temporal and inferior frontal lobes) is highly suggestive, but imaging is not confirmatory — CSF PCR is required. Empirical IV acyclovir (10 mg/kg q8h) should be started immediately in suspected HSE without waiting for PCR results, as delay worsens outcome.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.