2026 American Academy of Neurology Abstract Website

Objective:

To describe a rare case of HSV-1 encephalitis mimicking tumefactive MS in pregnancy. To highlight the diagnostic challenges, therapeutic priorities, and critical care strategies needed to optimize maternal and fetal outcomes.

Background:

Viral encephalitis and demyelinating disease can present with overlapping clinical and radiographic features. In pregnancy, altered immune responses and safety concerns further complicate diagnosis and management. Misattribution to demyelinating diseases may delay life-saving therapy.

Design/Methods:

A 31-year-old primigravida at 24 weeks gestation presented with seizures and fever, four weeks after a prior ICU admission for seizures where MRI demonstrated ovoid, periventricular lesions suggestive of MS. On readmission, repeat MRI revealed bilateral temporal lobe hyperintensities with hemorrhagic changes and parietal mass effect. Her course deteriorated rapidly, requiring decompressive hemicraniectomy, mechanical ventilation, tracheostomy, and PEG placement.

CSF analysis resulted in elevated protein, lymphocytic pleocytosis, and was positive for HSV-1 PCR. Autoimmune and paraneoplastic panels were negative, after previous empiric treatment with IVIG and PLEX. Treatment included IV acyclovir. Serial obstetric monitoring confirmed fetal viability.

Results:

Stabilization on follow-up imaging was observed. Patient's hospital stay was complicated by Pseudomonas Pneumonia. Long-term neurological recovery remains to be seen.

Hemorrhagic temporal lobe involvement and HSV PCR confirmation established the diagnosis of HSV-1 encephalitis. The outcome remains contingent on early ICU transfer, neurosurgical intervention, and multidisciplinary coordination between Neurology, Neurocritical care, Infectious disease, and Maternal-fetal medicine.

Conclusions:

HSV encephalitis may mimic tumefactive MS. Temporal lobe hemorrhage and positive PCR are key discriminators. A physiological condition like pregnancy may complicate neuro-inflammatory presentations.

Anchoring bias to a demyelination diagnosis risks delaying antiviral therapy. Early empiric acyclovir, coupled with neurosurgical and multidisciplinary management, was critical to maternal and fetal outcomes. The case highlights a knowledge gap in standardized approaches to encephalopathy with mass effect in pregnancy and the need for diagnostic algorithms for encephalopathy in pregnancy.