A 58-year-old man with cirrhosis presents to the emergency department with acute confusion, lethargy, and asterixis. EEG shows the pattern marked **A** in the diagram—generalized continuous polymorphic delta activity. Which of the following best explains the pathophysiological basis of this EEG finding?

Explanation

## Why "Bihemispheric cortical dysfunction due to diffuse metabolic or toxic encephalopathy" is right The pattern marked **A** — generalized continuous polymorphic delta activity (GPDA) — is the EEG hallmark of diffuse metabolic, toxic, or anoxic encephalopathy. GPDA is characterized by bilateral, symmetric, high-amplitude (50–200 μV) delta activity (0.5–3 Hz) with polymorphic morphology, accompanied by loss of the normal posterior dominant alpha rhythm. This pattern reflects bihemispheric cortical dysfunction rather than a focal lesion. In this patient with cirrhosis presenting with confusion and asterixis, hepatic encephalopathy (hyperammonemia) is the likely metabolic cause. The EEG severity correlates with clinical severity and may even precede clinical deterioration (Adams Neurology 12e Ch 16). ## Why each distractor is wrong - **Focal structural lesion in the left temporal lobe causing localized neuronal injury**: Focal delta activity over a single region (as shown in **B**) indicates a focal structural lesion. GPDA is bilateral and symmetric, not focal, ruling out this option. - **Deep midline lesion or elevated intracranial pressure causing frontal intermittent rhythmic activity**: This describes FIRDA (frontal intermittent rhythmic delta), shown as pattern **C**. FIRDA is intermittent, not continuous, and is associated with deep midline lesions or increased ICP—not diffuse metabolic encephalopathy. - **Normal variant of sleep-stage EEG with preserved posterior dominant rhythm**: Pattern **D** shows normal posterior alpha rhythm with intermittent theta in drowsiness. GPDA is abnormal and characterized by LOSS of the posterior dominant rhythm, not preservation of it. **High-Yield:** Generalized continuous polymorphic delta = diffuse bihemispheric dysfunction; always identify and treat the underlying metabolic cause (lactulose + rifaximin for hepatic encephalopathy, dialysis for uremia, sodium correction for hyponatremia). [cite: Adams Neurology 12e Ch 16; Harrison 21e Ch 425]