Abstracts

Rationale: To determine the diagnostic utility of EEG to clarify and differentiate between various causes of memory impairment.Methods: Study participants were adult patients referred to our laboratory with an EEG requisition diagnosis of memory impairment over a nine month period (June 2010-February 2011). Subjects were stratified based on age (18-64 vs >65 years old). Each participant had a 25-40 minute EEG. The background posterior rhythm was considered abnormal (slow) when it occurred at a frequency of <8 Hz. EEGs were also examined for presence or absence of reactivity to eye opening and closure, epileptiform features (sharp waves or spike wave discharges), and presence or absence of special features like triphasic wave complexes.Results: Forty-five participants met criteria for our study. See figure 1 for the distribution of abnormalities among the participants. Twenty-one of 45 participants (46.7%) had abnormal EEGs. Slowing of the background rhythm (<8 Hz) was found in 12% of the younger (18-64 years old) population and 45% of the older (>65 years old) population. Intermittent temporal slowing in the delta range was seen in 4% of the younger population and 25% of the older population. Temporal slowing predominantly occurred on the left side. Epileptiform features were found in 16% of the younger population and 5% of the older population. Periodic sharp wave complexes at a frequency of 1 Hz was seen in one subject in the older population. The majority of our younger patients studied had normal EEGs. Background slowing (PDR < 8Hz) was more frequently encountered in older patients, generally indicative of mild to moderate diffuse cerebral dysfunction. Intermittent temporal slowing was also more commonly noted in older patients. Younger patients had relatively more epileptiform features thus raising the possibility of an underlying seizure disorder that may be contributing to memory impairment. Generalized and bisynchronous periodic sharp wave complexes at approximately 1/sec were seen in one EEG raising the possibility of underlying idiopathic Creutzfeldt-Jakob disease (CJD).Conclusions: EEG is useful in the diagnostic workup of patients presenting with memory impairment, but caution should be exercised. This caveat is especially important in the elderly population given the evidence of a high background rate of EEG abnormalities in healthy individuals, such as slowing of background alpha and intermittent temporal slowing. While the EEG is useful for separating normal from abnormal cortical functioning, it is nonspecific. The EEG has a high sensitivity but low specificity in elucidating the etiology of memory impairment, but larger studies are needed.