Abstracts

Rationale: Alzheimer’s disease (DAT) is by far the most common etiology of incapacitating dementia in middle and late life. Clinical EEG is a non-invasive procedure, which is generally well tolerated, even by patients with cognitive impairment. EEGs are often carried out as part of the clinical assessment of patients with dementia. This study sought to characterize the clinical EEG findings in a carefully selected cohort of patients with DAT and no known history of seizures. Methods: Screening EEGs were performed prospectively in patients with mild to moderate DAT as part of their enrollment in a multicenter phase II clinical trial. Patients were 55 years or older with mild to moderate cognitive impairment (MMSE 12 to 24, and ADAS-Cog 14 to 42) who fulfilled DSM-IV criteria for DAT and NINCDS-ADRDA criteria for probable DAT. Patients with a known history of epilepsy, stroke, head trauma, cancer or major depression were excluded. Most patients were not on cholinomimetic agents at the time of the baseline EEG (except for 5 who were being tapered off). Results: 60-minute outpatient EEGs were performed in a total of 269 patients and were uniformly, and blindly interpreted by two fellowship-trained epileptologists at a single epilepsy center. Results were reported according to a consistent classification system employed for all EEGs at our center. Hyperventilation was routinely performed when feasible. Five patients were unable to cooperate with EEG recordings. In the remaining 264 patients the posterior background ranged from 5.5 to 13Hz, median 9Hz (26.8% of patients). EEGs were within normal limits in 48.9%. A slow <8Hz posterior background was seen in 7.2%, and in addition diffusely slow activity was seen in 14.8% of patients. Persistent regional slow activity in the low theta or delta range was predominantly temporal, and seen in 25.4% of patients; of whom approximately one fifth were noted to have occasional sharp transients, with a similar regional temporal distribution, intermixed with the temporal slowing. In addition, lateralized hemispheric slowing was seen in 3.8% of patients. Finally EEGs showed unequivocal epileptiform abnormalities in 10 of the 264 patients (3.8%), which were arising from the temporal lobe(s) in all but one patient with generalized interictal discharges. Conclusions: This study describes the findings of 60-minute outpatient EEG studies - which were performed prospectively, and interpreted in a uniform manner - in a well-characterized large cohort of patients with mild to moderate DAT, and no known history of seizures. The most common finding was a normal EEG for the patient's age. Slowing in the temporal region was the most common abnormality. Clear epileptiform abnormalities were seen in more than 3.5% of patients, higher than the reported rate in non-DAT normal adults. An epileptiform EEG is strongly predictive of future unprovoked seizures based on previous studies in this population. In addition, it may raise the clinical suspicion for subclinical or unrecognized seizures.