Temporary cognitive impairment as the only manifestation of a subclinical epileptiform electroencephalographic (EEG) discharge is a controversial phenomenon known as transitory cognitive impairment (TCI).132

Characteristic EEG changes include:133,134

• 3-Hz spike and wave discharges
• duration greater than 3 seconds
• prominent spike components
• early involvement of the frontocentral region

The precise EEG findings necessary to qualify a discharge as TCI are uncertain, however. Rugland135 observed that subclinical discharges impaired performance in 61% of the patients on a simple and a choice reaction time test, even though some discharges lasted only 1 second. Other studies have also claimed that impairment occurs with discharges of less than 3 seconds’ duration.136,137 Proponents claim that measurements of performance such as the modified Corsi’s Block Tapping Task,133 the writing-to-dictation test,138 and computer-based tests135 are sensitive to TCI. These tests, however, share a complexity that is more sensitive to all types of seizure activity.139,140

Most TCI is found in patients who also suffer from epilepsy, causing confusion as to whether long-term changes in cognitive function result from TCI or are effects of the comorbid epilepsy and the associated neuropathologic changes, seizures, and medications.

Also, the differences between TCI, interictal discharge in epilepsy patients, and subtle seizure are unclear. Aldenkamp et al.139 attempted to separate these entities and found poor cognitive performance only in the group experiencing subtle seizures, thereby challenging the distinction of TCI as a separate phenomenon.

Adapted from: Devinsky O and Tarulli A. Progressive cognitive and behavioral changes in epilepsy. In: Devinsky O and Westbrook LE, eds. Epilepsy and Developmental Disabilities. Boston: Butterworth-Heinemann; 2001;133–149.
With permission from Elsevier (www.elsevier.com).
Reviewed and revised May 2004 by Steven C. Schachter, MD, epilepsy.com Editorial Board.