Correct answer: C. Extreme Delta Brush (EDB)

This figure shows a run of 1Hz frontotemporally predominant generalized rhythmic delta activity (GRDA- frontal) with superimposed fast beta activity that has a stereotyped relationship to the delta waves, occurring maximally on the downstroke of the delta wave as shown below with arrows in a magnified version of the above EEG. Per the 2021 ACNS ICU EEG terminology, extreme Delta Brush is a specific subtype of RDA+F, where there is fast activity cycling with the rhythmic delta and having a stereotyped relationship to the delta wave and occurring on the upstroke, crest or the downstroke of the delta wave (1). It is divided into: Definite EDB: Consists of either abundant or continuous: A. RDA+F, in which the fast activity has a stereotyped relationship to the delta wave (e.g., always maximal on the upstroke, crest, or downstroke of the wave); OR B. PDs+F, in which each PD consists of a single blunt delta wave with superimposed fast activity, and in which the fast activity has a stereotyped relationship to the delta wave (i.e., periodic delta brushes). Possible EDB: Satisfying criterion A) or B) above EXCEPT either: i. only occasional or frequent (rather than abundant or continuous) in prevalence OR ii. the superimposed fast activity lacks a stereotyped relationship to the delta wave; continuous, invariant fast activity during RDA would fall into this category.

Correct answer: D. A & C

Anti-NMDAR encephalitis is an autoimmune disease caused by autoantibodies that target cell-surface NMDARs. Anti-NMDAR encephalitis patients typically present with viral prodrome, followed by subacute psychiatric symptoms such as delusions, hallucinations, movement abnormalities, and seizures. Previous studies have reported the extreme delta brush, a unique electroencephalography (EEG) pattern, in NMDAR encephalitis patients.(2) EDB is present in only one-third of anti-NMDAR encephalitis patients who have seizures(2,3). EDB was associated overall with increased length of hospital stay, increased ICU admission, and incidence of status epilepticus (4). The etiology of the EDB remains mainly unknown. However, it has been postulated when antibodies block/target the NMDAR, the rhythmic neuronal activity is disrupted, leading to the unique EDB pattern(4). Another theory suggests that delta activity is caused because of focal abnormalities in the brain, and the superimposition of the beta waves is related to the alterations of the NMDA receptors(4). EDB has been recently described in patients with anti-DPPX encephalitis. While extreme delta brushes are not anymore unique to anti-NMDAR encephalitis, its occurrence should trigger testing for autoimmune encephalitis in diagnostically unclear cases(5).