title: Using Poisson marginal models for investigating the effect of factors on interictal epileptiform discharge in patients with epilepsy.
abstract: BACKGROUND
  Epilepsy is a common, chronic neurological disorder that affects more than 40 million people worldwide. Epilepsy is characterized by interictal and ictal functional disturbances. The presence of interictal epileptiform discharges (IEDs) can help to confirm a clinical diagnosis of epilepsy, and their location and characteristics can help to identify the epileptogenic zone or suggest a particular epilepsy syndrome. The aim of this study is to determine the factors that affect IEDs.
  
  
  METHODS
  Poisson marginal model was done on 60 epileptic patients who were referred to Shefa Neurological Research Center, Tehran, for Video-Electroencephalogram (V-EEG) monitoring from 2007 to 2011. The frequency of IEDs was assessed by visual analysis of interictal EEG samples for 2 h.
  
  
  RESULTS
  The results show that among age, epilepsy duration, gender, seizure frequency and two common anti-epileptic drugs (Valproic acid and Carbamazepine), only age and epilepsy duration had statistical significant effect on IED frequency.
  
  
  CONCLUSIONS
  Investigating the factors affecting IED is not only of theoretical importance, but may also have clinical relevance as understanding the evolution of interictal epileptogenesis may lead to the development of therapeutic interventions. Generalized estimating equation is a valid statistical technique for studying factors that affect on IED. This research demonstrates epilepsy duration has positive and age has negative effect on IED which means that IED increases with epilepsy duration and decreases with increasing age. So for monitoring IED, we should consider both age and epilepsy duration of each patient.
authors.affiliation: Department of Biostatistics, Tarbiat Modares University, Tehran, Iran.
authors.forename: Mahsa
authors.initials: M
authors.lastname: Saadati
authors.forename: Soghrat
authors.initials: S
authors.lastname: Faghihzadeh
authors.forename: Sohrab Hashemi
authors.initials: SH
authors.lastname: Fesharaki
authors.forename: Marzieh
authors.initials: M
authors.lastname: Gharakhani
keywords: Epilepsy; Poisson marginal model; electroencephalogram; generalized estimating equations; interictal epileptiform discharge