PREVALENCE AND SIGNIFICANCE OF ELECTROENCEPHALOGRAPHIC ABNORMALITIES IN PATIENTS WITH SUSPECTED ORGANIC MENTAL SYNDROMES

Objective: To determine the prevalence of electroencephalogram (EEG) a bnormalities at different levels of cognitive impairment and to assess the possible diagnostic usefulness of the test. Design: Combined pros pective assessment of subjects receiving EEGs and retrospective chart review of symptoms and medications. Setting: Academic geriatric psychi atry service. Patients: 350 adults age 50 and above; 312 were patients being evaluated for possible organic mental syndrome and 38 were norm al controls. Measurements: All subjects had EEGs and Mini-Mental State Examinations (MMSE) performed at the time of the EEG. EEGs were rated for the presence and type of abnormality, and subjects were stratifie d according to the severity of impairment. Charts were reviewed by a p erson blinded to EEG results to determine clinical diagnosis and medic ations received. Main Results: Abnormal EEGs were significantly more c ommon among all patients (67%) in the study than among controls (11%), and the prevalence of abnormality increased with increasing impairmen t. Many demented patients with equivocal impairment (42%), and most wi th mild-to-moderate impairment (65%) had abnormal EEGs. An abnormal EE G was not indicative of dementia even when clear cognitive impairment was present, since patients with depression frequently also had abnorm al EEG results. Conclusions: These findings suggest that the EEG is a moderately sensitive but non-specific indicator of brain dysfunction i n the elderly. The significance of abnormalities among patients with e quivocal impairment should be more fully assessed by longitudinal foll ow-up to determine if greater cognitive impairment develops.