title: A meta-analysis of white matter changes in temporal lobe epilepsy as studied with diffusion tensor imaging.
abstract: OBJECTIVE
  Diffusion tensor imaging (DTI) is used increasingly to study white matter integrity in people with temporal lobe epilepsy (TLE). Most studies report fractional anisotropy (FA) decrease and mean diffusivity (MD) increase in multiple white matter regions. The disturbance of white matter integrity varies across studies and between regions. We aimed to obtain a more consistent estimate of white matter diffusion characteristics and relate these to the distance from the seizure focus.
  
  
  METHODS
  Studies comparing diffusion characteristics of people with epilepsy with those of healthy controls were systematically reviewed and quantified using random and mixed effects meta analysis. In addition to the overall meta-analysis, pooled FA and MD differences were determined per hemisphere and white matter category separately.
  
  
  RESULTS
  We included 13 cross-sectional studies. The pooled FA difference for all white matter was -0.026 (95% confidence interval [CI] -0.033 to -0.019) and MD difference was 0.028 × 10(-3) mm(2)/s (95% CI 0.015-0.04). FA was reduced significantly in people with TLE compared with healthy controls in both ipsilateral (mean difference -0.03) and contralateral white matter (-0.02). MD was significantly increased ipsilaterally and contralaterally. MD differed significantly between white matter connected to the affected temporal lobe and remote white matter.
  
  
  CONCLUSIONS
  The meta-analysis provides a better estimation of the true diffusion characteristics. White matter structural integrity in TLE is disturbed more severely in the ipsilateral than in the contralateral hemisphere, and tracts closely connected with the affected temporal lobe are most disturbed. The exact underlying mechanisms remain to be elucidated.
authors.affiliation: Department of Pediatric Neurology, Rudolf Magnus Institute of Neuroscience, University Medical Center Utrecht, Utrecht, The Netherlands. wim@invivonmr.uu.nl
authors.forename: Willem M
authors.initials: WM
authors.lastname: Otte
authors.forename: Pieter
authors.initials: P
authors.lastname: van Eijsden
authors.forename: Josemir W
authors.initials: JW
authors.lastname: Sander
authors.forename: John S
authors.initials: JS
authors.lastname: Duncan
authors.forename: Rick M
authors.initials: RM
authors.lastname: Dijkhuizen
authors.forename: Kees P J
authors.initials: KP
authors.lastname: Braun
mesh_terms: D001921:Brain / Q000378:metabolism / Q000473:pathology*; D001931:Brain Mapping; D003430:Cross-Sectional Studies; D016206:Databases, Bibliographic / Q000706:statistics & numerical data; D056324:Diffusion Tensor Imaging; D004833:Epilepsy, Temporal Lobe / Q000473:pathology*; D005260:Female; D006801:Humans; D008297:Male; D009413:Nerve Fibers, Myelinated / Q000473:pathology*