title: "Ictal" lateralized periodic discharges.
abstract: OBJECTIVE
  Whether lateralized periodic discharges (LPDs) represent ictal or interictal phenomena, and even the circumstances in which they may represent one or the other, remains highly controversial. Lateralized periodic discharges are, however, widely accepted as being ictal when they are time-locked to clinically apparent symptoms. We sought to investigate the characteristics of "ictal" lateralized periodic discharges (ILPDs) defined by time-locked clinical symptoms in order to explore the utility of using this definition to dichotomize LPDs into "ictal" and "nonictal" categories.
  
  
  METHODS
  Our archive of all continuous EEG (cEEG) reports of adult inpatients undergoing prolonged EEG monitoring for nonelective indications between 2007 and 2011 was searched to identify all reports describing LPDs. Lateralized periodic discharges were considered ILPDs when they were reported as being consistently time-locked to clinical symptoms; LPDs lacking a clear time-locked correlate were considered to be "nonictal" lateralized periodic discharges (NILPDs). Patient charts and available neuroimaging studies were also reviewed. Neurophysiologic localization of LPDs, imaging findings, presence of seizures, discharge outcomes, and other demographic factors were compared between patients with ILPDs and those with NILPDs. p-Values were adjusted for false discovery rate (FDR).
  
  
  RESULTS
  One thousand four hundred fifty-two patients underwent cEEG monitoring at our institution between 2007 and 2011. Lateralized periodic discharges were reported in 90 patients, 10 of whom met criteria for ILPDs. Nine of the patients with ILPDs demonstrated motor symptoms, and the remaining patient experienced stereotyped sensory symptoms. Ictal lateralized periodic discharges had significantly increased odds for involving central head regions (odds ratio [OR]=11; 95% confidence interval [CI]=2.16-62.6; p=0.018, FDR adjusted), with a trend towards higher proportion of lesions involving the primary sensorimotor cortex (p=0.09, FDR adjusted).
  
  
  CONCLUSIONS
  When defined by the presence of a time-locked clinical correlate, ILPDs appear to be strongly associated with a central EEG localization. This is likely due to cortical irritability in central head regions having greater propensity to manifest with positive, clinically apparent, and time-locked symptoms. Thus, dichotomization of ILPDs and NILPDs on this basis principally reflects differences in underlying anatomical locations of the periodic discharges rather than providing a clinically salient categorization.
authors.affiliation: Feinberg School of Medicine, Northwestern University, 710 N Lakeshore Drive, Chicago, IL 60611, USA. Electronic address: neilsg@fsm.northwestern.edu.
authors.forename: Indranil
authors.initials: I
authors.lastname: Sen-Gupta
authors.affiliation: Feinberg School of Medicine, Northwestern University, 710 N Lakeshore Drive, Chicago, IL 60611, USA. Electronic address: s-schuele@northwestern.edu.
authors.forename: Stephan U
authors.initials: SU
authors.lastname: Schuele
authors.affiliation: Feinberg School of Medicine, Northwestern University, 710 N Lakeshore Drive, Chicago, IL 60611, USA. Electronic address: m-macken@northwestern.edu.
authors.forename: Micheal P
authors.initials: MP
authors.lastname: Macken
authors.affiliation: Feinberg School of Medicine, Northwestern University, 710 N Lakeshore Drive, Chicago, IL 60611, USA. Electronic address: m-kwasny@northwestern.edu.
authors.forename: Mary J
authors.initials: MJ
authors.lastname: Kwasny
authors.affiliation: Feinberg School of Medicine, Northwestern University, 710 N Lakeshore Drive, Chicago, IL 60611, USA. Electronic address: e-gerard@northwestern.edu.
authors.forename: Elizabeth E
authors.initials: EE
authors.lastname: Gerard
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000927:Anticonvulsants / Q000627:therapeutic use; D001931:Brain Mapping; D004569:Electroencephalography; D004827:Epilepsy / Q000188:drug therapy / Q000503:physiopathology*; D005260:Female; D007839:Functional Laterality; D006801:Humans; D008137:Longitudinal Studies; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D010507:Periodicity
chemical_list: D000927:Anticonvulsants
keywords: Continuous EEG monitoring; Epilepsia partialis continua; ICU EEG; Ictal–interictal continuum; LPDs; PLEDs; Semiology