Assessment of drowsiness in epilepsy patients receiving chronic antiepileptic drug therapy

Drowsiness is a common complaint among patients with epilepsy taking antiepileptic drugs (AEDs) and may be of particular importance because of the potential effects on cognitive abilities. We used a novel EEG‐based measure (the Awake Maintenance Task, AMT) to determine objectively whether patients on chronic, stable AED therapy had impaired ability to maintain wakefulness. Thirty patients receiving AEDs [carbamazepine (CBZ), phenytoin (PHT), phenobarbital (PB), valproate (VPA)] were compared to 35 healthy controls, 12 seizure patients not taking AEDs, and 16 patients with multiple sclerosis. A structured EEG recording was conducted under controlled conditions, and subjects were tested to determine their ability to maintain wakefulness during a 6‐min unstimulated trial. Testing also included Digit Symbol, auditory reaction time, and subjective measures of fatigue or sleepiness [Profile of Mood States (POMS), Stanford Sleepiness Scale (SSS)]. Patients receiving AEDs had a mean total drowsiness score of 101 s compared with < or = 12 s for each of the three control groups (P < 0.001). One third of the AED‐treated patients had > 120 s of drowsiness, in contrast to only 1 of 63 controls (p < 0.001). Among patients receiving AEDs, objective EEG drowsiness did not correlate with AED levels or performance measures. Untreated seizure patients had significantly greater complaints of lack of vigor despite a near absence of objective drowsiness on the AMT. These results suggest that epilepsy patients receiving chronic AED therapy have impaired ability to maintain wakefulness. Patient self‐reports of AED‐related sleepiness may not accurately represent this problem.