Interictal spiking in adult newly-diagnosed focal epilepsy of unknown cause: The effect of age.

OBJECTIVE: To assess the yield of interictal EEG spiking in standard and whole-night sleep EEGs in elderly subjects with recent-onset focal seizures compared to younger patients. METHODS: Detection of interictal epileptiform abnormalities (IEAs) and rating of mean spike index (number of interictal discharges/minute) values for different sleep stages (NREM stages 1-2 and 3-4 and REM sleep) in standard EEG (S-EEG) and 24-h ambulatory EEG (A-EEG) at first referral in three groups of thirty consecutive outpatients [aged 20-39 (young), 40-59 (adults) and ⩾60years (elderly)], retrospectively selected according to a subsequent diagnosis of focal epilepsy of unknown cause, no sleep disorders or drugs or comorbidities affecting sleep and EEG. RESULTS: Elderly subjects showed a lower rate of IEAs on S-EEG (p<0.01) but a higher propensity for spiking during deep NREM sleep, 11/30 showing IEAs exclusively during stages 3-4. Mean spike index showed a significant increase in IEAs between sleep stages 1-2 and 3-4 in the elderly subjects (p<0.001). CONCLUSIONS: A significant association emerged between IEAs during deep sleep and age (p<0.001). SIGNIFICANCE: EEG recordings covering deep NREM sleep should be recommended when IEAs detection is needed to support a diagnosis of epilepsy in elderly subjects.