The incidence of focal and non-focal EEG abnormalities in clinical epilepsy

Abstract

1. 1. A group of patients with clinical epilepsy have been studied in various centers across Canada. 2. 2. In 428 civilian patients, 38 per cent had focal EEG abnormalities. 3. 3. In 262 veterans and service patients who were carefully studied, 66.5 per cent had focal EEG abnormalities. 4. 4. In another group of 175 veterans, 39.5 per cent had focal EEG abnormalities. 5. 5. In the total series of 865 patients, 47 per cent had focal EEG abnormalities. 6. 6. This figure was identical with the percentage of focal EEG abnormalities found in 2 previous groups of patients studied at the Montreal Neurological Institute. 7. 7. In a total of 2648 patients with clinical epilepsy, focal EEG abnormalities were the largest single group of EEG disturbances. 8. 8. The percentage of focal disturbances uncovered depends to a considerable extent on the technique and care used in doing localization studies. 9. 9. Eighty-one per cent of patients with clinically focal seizures had a focal EEG abnormality. 10. 10. Although 80 per cent of patients with petit mal attacks had bilaterally synchronous EEG disturbances, the latter also occurred in 53 per cent of patients who had grand mal attacks only. This form of discharge therefore, although commonly seen in petit mal, is by no means pathognomonic. Nor is it only seen in idiopathic epilepsy, though they are very frequently associated. 11. 11. Diffuse dysrhythmias were most frequently associated with patients who had only grand mal seizures. 12. 12. Bilaterally synchronous disturbances were much more common in patients whose seizures began before the age of 25 years. 13. 13. Focal EEG abnormalities were much more common in patients over 25 years of age and particularly if the attacks began after the age of 25 years. 14. 14. Diffuse dysrhythmias were evenly distributed in all age groups. 15. 15. Borderline or normal EEG records were seen more frequently in patients with grand mal attacks only and in older patients particularly after the age of 56 years. 16. 16. The lowest percentage of normal and borderline records were seen in patients with petit mal and in infants and young children.