Value of long-term electroencephalogram in diagnosing epilepsy

BACKGROUND: Routine electroencephalogram (EEG) usually cannot accurately reflect the discharge of epileptic patients due to the short examination, and long-term EEG can make up the shortcoming. OBJECTIVE: To comparatively analyze the long-term EEG of epileptic and non-epileptic patients, and investigate the values of long-term EEG in the diagnosis and differential diagnosis of epilepsy. DESIGN: A case-controlled study. SETTING: Ningjin County People’s Hospital. PARTICIPANTS: Totally 122 patients with epilepsy (epilepsy group) were selected from the EEG room of Ningjin County People’s Hospital from January 2000 to December 2006, including 76 males and 44 females, 7 months to 78 years of age, the disease course ranged from 7 days to 7.5 years, and they all according with the standards for epilepsy set by the International Association for Epilepsy in 1997. Meanwhile, 118 patients with non-epileptic paroxysmal diseases were selected as the control group, including 71 males and 47 females, 2.5-87 years of age, the disease course ranged from 3 days to 7.5 years. Informed contents were obtained from all the subjects. METHODS: OXFORD GATE WAY 2000 16-lead portable EEG recorder was used for 24-hour electroencephalographic procedure. The patients could move normally during the monitoring, their activities, sleeping conditions, time and manifestations of seizures were recorded in details. In the next day, EEG at wake was recorded for 10 minutes, followed by 3-minute hyperventilation and open/close eye induction test, the phases of non-rapid eye movement (Ⅰ-Ⅳ) and rapid eye movement were performed using EEG at sleep according to the international EEG standard. The abnormal rates of EEG epileptic discharge at wake and sleep at different sites were calculated. MAIN OUTCOME MEASURES: Abnormal rate of long-term EEG at wake and sleep in both groups; Epileptic discharge at different sleeping phases in both groups; Abnormal rates of EEG epileptic discharge at wake and sleep at different sites in the epilepsy group. RESULTS: All the 122 patients with epilepsy and 118 patients with paroxysmal diseases were involved in the final analysis of results. ① Comparison of abnormal rate of long-term EEG at wake and sleep: In the epilepsy group, the abnormal rate of EEG at wake was obviously lower than that at sleep (68%, 91%, P < 0.01). In the control group, the abnormal rate of EEG at wake and sleep had no obvious difference (P > 0.05). ② Results of epileptic discharge at different sleeping phases: In the epilepsy group, the epileptic discharge occurred at Ⅰ-Ⅱ phases of sleep cycle in 88.1%, and at Ⅲ-Ⅳ in 11.9%; In the control group, the epileptic discharge occurred at Ⅰ-Ⅱ phases of sleep cycle in 91.7%, and at Ⅲ-Ⅳ phases in 8.3% (1/12). ③ Comparison of the abnormal rates of EEG epileptic discharge at wake and sleep at different sites in the epilepsy group: The abnormal rates of epileptic discharge at frontal lobe and temporal lobe at sleep were obviously higher than those at wake (21.3%, 24.6%; 10.7%, 11.7%, P < 0.01), while there were no obvious differences at wake and sleep at occipital lobe, parietal lobe (P > 0.05). CONCLUSION: Long-term EEG has great importance in the diagnosis and differential diagnosis of epilepsy, especially that it increases the detective rate of discharge by several cycles of sleep derivation. This method also provides important reference for the allocation of epileptic focus.