Focal seizures and EEG: prognostic considerations.

The goal of this study was to determine whether the EEG could predict if patients with focal seizures would eventually be uncontrolled (U), more than two seizures per month, or be controlled (C), fewer than two seizures per year. Using these latter criteria, U and C patients were randomly selected from our files, 150 in each of these two groups; 804 EEGs were found in the U and 674 in the C group. Excluded were patients with generalized epilepsy and also the benign epilepsies of childhood. Age was an important factor since patients 5-18 yrs old were more often under good control (C group), and those 21-48 yrs of age were more often under poor control (U group). With rare exceptions, focal spikes and focal slow waves in every area were much more often seen in U patients than C patients. No spikes or rare spikes appeared especially in the controlled patients, and many or very many spikes in the uncontrolled patients, mainly on the first or second EEG. No slow waves or a mild degree of slowing was seen especially in the C patients, while greater degrees of slow wave abnormalities were noted much more often in the U patients. For conditions to identify the C group, the best predictors were no spikes or rare spikes, especially on the first or second EEG, properly identifying two-thirds of the C patients and misidentifying only one-fourth of the U group. To identify the U patients on any EEG, many or very many spikes at any location or frontal spikes correctly designated a U patient in 84%, but incorrectly predicted a C patient as uncontrolled in 29%. For the first or second EEG, these values were 61% and 21%. Thus, the EEG, especially by its first or second record, can predict well the probable future of the uncontrolled patient, so that extraordinary means may be instituted early to avoid a deteriorating condition. When complete EEGs are done with sleep records and the results are quantified, reasonable prediction of eventual outcome can usually occur that is much more timely than waiting over 9 yrs, using only clinical data.