A 58-year-old man is admitted with acute-onset fever, altered mental status, and seizures. EEG shows the pattern marked **A** in the diagram—bilateral independent periodic sharp-wave complexes firing at different rates over each hemisphere, with markedly suppressed background activity. Which of the following is the MOST IMPORTANT immediate diagnostic and therapeutic consideration?

Question

Accepted Answer

C. Empirical acyclovir therapy pending HSV PCR and lumbar puncture, as herpes simplex encephalitis is the classic association with this pattern. ## Why option 1 is correct

Bilateral independent PLEDs (marked **A**) constitute one of the most ominous EEG patterns in adult neurology and are classically associated with **herpes simplex encephalitis**, particularly with temporal predominance. The pattern reflects widespread, severe bihemispheric cortical injury from acute processes such as HSV, CMV, bacterial meningitis, or anoxic-hypoxic injury. In a febrile patient with encephalopathy and seizures, empirical acyclovir must be initiated immediately pending confirmatory HSV PCR from cerebrospinal fluid and neuroimaging, as delays in treatment of HSV encephalitis significantly worsen prognosis. This is the standard-of-care approach endorsed by critical care neurology guidelines (Niedermeyer's Electroencephalography 7e; ACNS Standardised Critical Care EEG Terminology 2021).

## Why each distractor is wrong

- **Option 2**: While seizure management with benzodiazepines is important, suppressing the periodic discharges themselves rarely alters the dismal prognosis dictated by the underlying bihemispheric lesion. The priority is identifying and treating the cause (e.g., HSV), not the EEG pattern alone.
- **Option 3**: Although neuroimaging is part of the workup, bilateral subdural hematomas would typically show mass effect and midline shift on imaging and would not produce this specific EEG pattern. BiPLEDs reflect diffuse cortical injury, not focal mass effect.
- **Option 4**: While metabolic encephalopathy can occasionally produce periodic discharges, hyperammonemia is not the classic association with BiPLEDs. The pattern is dominated by acute bihemispheric infections (especially HSV) and anoxic-hypoxic injury, not metabolic derangement alone.

**High-Yield:** BiPLEDs = bilateral independent foci at different rates + different morphologies; classic association is HSV encephalitis; mortality 60–90%; empirical acyclovir is the urgent first step.

[cite: Niedermeyer's Electroencephalography 7e; ACNS Standardised Critical Care EEG Terminology 2021]

Answer

A. Immediate benzodiazepine and phenytoin loading to suppress the periodic discharges and prevent seizure evolution

Answer

B. Metabolic panel and ammonia level, as this pattern is pathognomonic for hyperammonemic encephalopathy

Answer

D. Neuroimaging to rule out bilateral subdural hematomas, as this pattern indicates acute mass effect

Explanation

Why option 1 is correct

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