Usefulness of EEG for the differential diagnosis of possible transient ischemic attack

•FSWA was the commonest EEG abnormality in patients with possible TIA.•FSWA in the early EEG did not distinguish TIA from epileptic seizure patients.•The majority of epileptic seizure patients did not have EA in the early or late EEG.•In patients with seizures, FSWA in the early EEG was more common than EA.•FSWA in late EEG was more likely in patients with an epileptic seizure than with a TIA. EEG value in possible transient ischemic attacks (TIA) is unknown. We aim to quantify focal slow wave activity (FSWA) and epileptiform activity (EA) frequency in possible TIA, and to analyse its contribution to the final diagnosis of seizures and/or definitive TIA. Prospective longitudinal study of possible TIA patients evaluated at a tertiary centre during 36 months and with 1–3 months follow-up. EEG was performed as soon as possible (early EEG) and one month later (late EEG). A stroke neurologist established final diagnosis after reassessing all clinical and diagnostic tests. 80 patients underwent an early EEG (45.8 h after possible TIA): 52 had FSWA and 6 of them also EA. Early FSWA was associated with epileptic seizure or definitive TIA final diagnosis (p = .041). Patients with these diagnoses had more frequently early FSWA (19/23; 82.6%) than EA (6/23; 26.1%). 6/13 (46.2%) patients with epileptic seizure final diagnosis had EA. In the late EEG, 43 (58.1%) patients demonstrated persistent FSWA and 3 of them also EA. Persistent FSWA in the late EEG was more frequent in seizures than in TIA patients (91.7% vs. 45.5%). FSWA disappearance was associated with acute vascular lesion on neuroimage. FSWA was the commonest EEG abnormality found in the early EEG of patients with possible TIA, but did not distinguish between TIA and seizure patients. In patients with seizures, FSWA was more common than EA and its presence in the late EEG was more likely in patients with epileptic seizures than with TIA. The majority of possible TIA patients with the final diagnosis of epileptic seizures do not have EA in the early or late EEG.