A 22-year-old woman presents to the ICU with a 3-week history of progressive psychiatric symptoms (paranoia, agitation, catatonia), followed by seizures, orofacial dyskinesias, and autonomic instability (fever, tachycardia, hypertension fluctuations). CSF analysis shows lymphocytic pleocytosis with oligoclonal bands. Anti-NMDAR IgG is detected in CSF. EEG shows the pattern marked **A** in the diagram—rhythmic 1–3 Hz delta activity with superimposed 20–30 Hz beta bursts. Which of the following best describes the clinical significance of this EEG finding?
A. It is diagnostic of neonatal encephalopathy and excludes autoimmune etiology
B. It is pathognomonic for anti-NMDA receptor encephalitis and indicates need for urgent tumor screening and immunotherapy
C. It correlates with prolonged illness duration and worse prognosis, seen in approximately 30% of anti-NMDA receptor encephalitis patients
D. It represents a benign variant seen in 70% of anti-NMDA receptor encephalitis cases with excellent prognosis
Explanation
Why option C is right
The extreme delta brush pattern (marked A) is a characteristic but not pathognomonic EEG finding in anti-NMDA receptor encephalitis, occurring in approximately 30% of patients. This pattern—consisting of rhythmic 1–3 Hz delta activity with superimposed 20–30 Hz beta bursts—correlates with prolonged illness duration and worse prognosis. While highly suggestive in the appropriate clinical context (young woman with psychiatric symptoms, seizures, movement disorders, autonomic instability, and positive anti-NMDAR IgG in CSF), it is not present in all cases and does not itself establish diagnosis. However, when present, it carries prognostic significance indicating more severe disease course. (Harrison Internal Medicine 21e; Lancet Neurol 2019)
Why each distractor is wrong
Option A: While the extreme delta brush is highly suggestive of anti-NMDA receptor encephalitis in the clinical context shown, it is not pathognomonic—it occurs in only ~30% of cases, and diagnosis is confirmed by anti-NMDAR IgG detection in CSF, not by EEG pattern alone. The statement overstates the diagnostic specificity.
Option B: This is factually incorrect. The extreme delta brush is seen in approximately 30% of anti-NMDA receptor encephalitis patients, not 70%, and its presence correlates with worse prognosis, not excellent prognosis.
Option D: The extreme delta brush pattern resembles neonatal delta brushes morphologically but occurs in adult autoimmune encephalitis, not neonatal encephalopathy. Its presence in this clinical context (positive anti-NMDAR IgG, psychiatric symptoms, seizures, movement disorders) is entirely consistent with autoimmune etiology and does not exclude it.
High-YieldNEET PG
Extreme delta brush on EEG in anti-NMDA receptor encephalitis = ~30% of cases, correlates with prolonged illness and worse prognosis; diagnosis confirmed by anti-NMDAR IgG in CSF, not EEG alone.
Harrison Internal Medicine 21e; Lancet Neurol 2019
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