Patients aged 2 to 85 (mean 32) years whose focal seizures were uncontrolled (U) (more than 2 seizures per month) and a group with controlled seizures (C) (fewer than 2 seizures per year), 150 in each group, were randomly selected from files at the University of Illinois Medical Center, Chicago, and EEGs in the two groups (804 in U group and 674 in C group) were examined for their predictive value of seizure control. Patients with generalized epilepsy and benign epilepsies of childhood were excluded. Younger patients (5-18 yrs) were generally better controlled than those 21-48 years of age, and seizure intractability became more prevalent in the 20 to 40 year age group. Focal spikes and focal slow waves were more common in U patients than C patients. Many spikes or slow waves occurred in EEGs of U patients and no or rare spikes or slow waves in C patients’ records. Predictors of C focal seizures were no or rare spikes, especially on the first or second EEG. U patients were correctly identified by many spikes (at least one/10 sec) at any location or frontal spikes in 84% cases (61% with 1st or 2nd EEG), but 29% (21% in 1st or 2nd EEGs) were incorrectly identified as U and seizures were controlled. The EEG is a useful predictor of prognosis of the uncontrolled focal seizure patient, and should be a guide to early more effective therapy. 
COMMENT. Based on frequent spike occurrence in first or second EEG recordings in patients with focal seizures, a positive prediction of uncontrolled seizures and poor prognosis is likely in 61% but a false positive may occur in 21%. In any EEG recording, the true positives are 84% and false positives 29%. Seizure intractability is especially frequent in the 20 to 40 year age group. Patients with rare spikes have less frequent less severe focal seizures and a lower incidence of secondarily generalized tonic-clonic seizures.