Triphasic waves in a psychiatric population: a retrospective study.

In a retrospective study of 15.326 EEGs performed from 1983 to 1992 in a psychiatric institute, 83 EEGs (62 patients-13 men and 49 women ranging in age from 59 to 90 years, with a mean age of 74 years) had triphasic waves (TWs). All 62 patients were awake, though they were often confused. Most (n = 56) had dementia, usually severe; 15 also had delirium. There were six nondemented patients (age range, 59-79 years, with a mean age of 67 years). Infrequent etiologies included neuroleptic malignant syndrome (n = 1) and hepatic encephalopathy (n = 1); in four, the cause was uncertain, although all were receiving lithium. EEG features analyzed included frequency of background rhythms, distribution of the TWs, periodicity, and epileptiform abnormalities. Background rhythms were slow in all but seven patients (mean, 6.2 +/- 1.7 [SD] Hz). TWs were maximal posteriorly in 47 patients and anteriorly in six and were diffuse in nine. Neuroimaging studies showed prominent posterior abnormalities in only one case. Periodicity was prominent in four patients; in two the TWs were maximal anteriorly. Interictal epileptiform activity was present in six, a history of seizures in eight, and myoclonus in four. TWs are uncommon in a psychiatric population; they occur primarily in elderly, severely demented patients. They are usually associated with background slowing, are often maximal posteriorly, and occasionally are periodic.