Extreme delta brush

Electroencephalography (EEG) remains an essential neurodiagnostic tool, even in the magnetic resonance imaging/positron emission tomography era. Certain EEG patterns are diagnostic of specific epilepsy syndromes, such as the 3 Hz spike-and-wave seen in childhood absence epilepsy. Extreme delta brush is a distinctive EEG pattern described in autoimmune encephalitis, particularly anti-NMDAR encephalitis. It consists of continuous delta waves with superimposed fast activity, usually in the beta range (13–40 Hz) [Figure 1]. This pattern is typically symmetric, synchronous and widely distributed across the scalp. It does not fluctuate with sleep-wake cycles, external stimuli or movement artefacts.Figure 1: Electroencephalography of 10 years old female showing delta brush (arrow), diagnosed with anti-NMDAR encephalitisAutoimmune encephalitis can have non-specific presentations and may initially be misdiagnosed as a psychiatric illness. However, the presence of extreme delta brush on EEG is a highly specific clue pointing towards this diagnosis. It may also be seen in severe hypoxic-ischemic injury, Creutzfeldt–Jakob disease and metabolic or toxic encephalopathies, though these conditions often show different clinical profiles and EEG features. In paediatric intensive care units (PICUs), benzodiazepine infusion may produce beta activity but lacks the rhythmic delta-beta structure of extreme delta brush. Clinicians should familiarise themselves with this pattern, particularly in the PICU setting. Recognising extreme delta brush can support early diagnosis and appropriate management of autoimmune encephalitis. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.