Characteristic EEG findings in ring 20 syndrome as a diagnostic clue

Objective: To review the EEG features of ring 20 syndrome in two patients to disclose the characteristic pattern of this syndrome. The features of our cases and 24 patients reported in the literature will be discussed.

Subjects and methods: Report of two patients and review of literature.

Results: The two patients had intractable epilepsy since childhood. Their clinical seizures were mostly complex partial seizures. Often the patients seizures were of prolonged duration. Ictal EEG revealed characteristic slow waves, and sharp waves. The slow waves were (1) usually synchronous high-voltage slow waves with or without a spike component predominantly in the frontal and frontopolar areas, (2) sometimes showed a change in frequency every several seconds, (3) continued for a long period, and (4) easily spread diffusely. The sharp waves were 5–6 Hz irregular and diffuse discontinuous sharp waves, and sometimes appeared predominantly in the centroparietal area. The clinical seizure pattern and EEG findings were similar in the 24 published cases.

Conclusions: These EEG findings may be a characteristic feature of ring 20 syndrome and thus may be useful as a diagnostic clue.