Centroparietal periodic sharp-wave discharges and biphasic complexes: Novel EEG biomarkers for early diagnosis of Rasmussen encephalitis

Rasmussen encephalitis (RE) is a rare, chronic inflammatory brain disorder that predominantly affects one hemisphere in children. It is characterized by progressive neurological deterioration and refractory seizures. Early diagnosis remains challenging due to nonspecific initial symptoms and diagnostic features that overlap with other neurological conditions. To identify early and specific EEG patterns that may support timely initiation of immunomodulatory therapies. Continuous long-term video-EEG monitoring was repeatedly conducted in a female patient who experienced her first seizures at age 16, soon after a febrile illness. Identification of two distinctive EEG patterns—focal periodic sharp-wave discharges and biphasic complexes—allowed early diagnosis prior to the onset of severe deficits or epilepsia partialis continua. The biphasic complexes occurred alongside unilateral slow-wave activity, whereas focal periodic sharp-wave discharges were initially observed on an otherwise normal background. The biphasic complexes appear to herald evolution to the acute phase of the disease. Prompt immunomodulatory therapy (intravenous immunoglobulin followed by adalimumab) successfully halted disease progression, nearly normalized EEG background activity, and reduced seizure frequency. This case underscores the prognostic value of recurrent focal periodic sharp-wave discharges and biphasic complexes as prodromal EEG biomarkers for RE, aligning with one prior study linking these biphasic complexes to early-stage disease (Beaumanoir et al., 1997). Early recognition of these patterns is essential. Early initiation of immunotherapy may prevent irreversible neurological damage, highlighting the critical role of recognizing these electrographic patterns for timely diagnosis and intervention. • Rasmussen encephalitis (RE) is often diagnosed during the acute phase. • EEG findings are crucial when an MRI appears normal. • EEG findings, such as focal periodic sharp wave discharges and biphasic complexes, may flag early RE. • EEG patterns differentiate RE from focal cortical dysplasia and other focal epilepsies. • Early recognition enables prompt immunotherapy, which may help slow disease progression.