Interictal electroencephalography in patients with epilepsy in northwestern Nigeria

Background: Different studies have reported various frequencies of electroencephalographic (EEG) abnormalities in patients with epilepsy. There is, however, a paucity of data on EEG in Nigeria; hence, the need for this study. Objective: The objective of the following study was to evaluate interictal EEG pattern in patients with epilepsy in Kano, Northwestern Nigeria. Subjects and Methods: A cross-sectional study involving the analysis of EEGs of consecutive patients with clinical diagnosis of epilepsy over a 5 year period at two diagnostic centers in Kano, northwestern Nigeria. Information on socio-demographic and seizure characteristics was obtained. The recordings from patients were obtained using the standard methods and interpreted by two of the investigators. The International Federation of Societies for Electroencephalography and Clinical Neurophysiology definition of interictal epileptiform discharges (interictal epileptiform activity [IEA]) was adopted for the study. Result: Out of 2219 patients referred for EEG at the two diagnostic centers during the study period, 2041 (92%) patients had a clinical diagnosis of epilepsy. Their age ranged between 0.04 and 75 years, with a mean age of 22.8 ± 14.9 years. Overall, EEG was abnormal in 1178 (57.7%) and 919 (45.1%) had an epileptiform pattern. A total of 1691 patients had hyperventilation (HV) and response to HV was unremarkable in 1286 (76%) of them. Out of 405 who had remarkable changes on HV; 302 had increase in epileptiform discharges, whereas 103 had abnormal discharges only on HV. Seventeen (89.5%) out of 19 patients with 3 Hz spike and wave complexes had activation by HV. The most common IEA were focal spike/sharp and wave and generalized spike/sharp and slow waves. More antiepileptic drug (AED) naive patients (678) than those that were on AED (500) had EEG abnormality and the difference was statistically significant, P < 0.001. Conclusion: The study showed that the occurrence of interictal EEG abnormality in patients with epilepsy was about 58%. The proportion of interictal epileptiform discharges was 45% in routine first EEG studies. Among those with epileptiform activity, generalized sharp and wave complexes and focal sharp and slow wave complexes were the most common findings.