title: Linking MRI hyperintensities with patterns of neuropsychological impairment: evidence for a threshold effect.
abstract: OBJECTIVE
  Leukoaraiosis (LA) might interrupt intra- and interhemispheric communication and thus induce cognitive impairments and dementia. It remains unclear, however, if there is a volume threshold of LA that is needed before either the signs of dementia and/or a specific pattern of neuropsychological impairment become manifest. Roman et al has suggested that 25% of white matter may need to be involved before white matter alterations influence the clinical signs associated with dementia. The purpose of this study is to ascertain the threshold of MRI-LA as measured with a visual rating scale needed to induce specific patterns of neuropsychological impairment associated with dementia.
  
  
  METHODS
  One hundred fifteen patients with dementia received a comprehensive neuropsychological examination and the severity of MRI-LA was measured using a 40-point LA scale.
  
  
  RESULTS
  Patients were categorized into low (mean LA=4.21+/-2.92; 3.22%-17.82%), moderate (mean LA=12.58+/-2.54; 25.01%-37.80%), and severe (mean LA=22.36+/-4.04; 45.80%-66.00%) LA groups. Patients in the mild LA group obtained markedly lower scores on tests of episodic memory compared with working memory, a neuropsychological profile often associated with Alzheimer disease. Patients with moderate LA displayed equal impairment on neuropsychological tests. Patients in the severe LA group obtained significantly lower scores on tests of working memory as compared with episodic memory.
  
  
  CONCLUSIONS
  These data provide evidence that a threshold of moderate MRI-LA as measured with a visual rating scale is associated with greater and/or equal impairment on tests of working memory versus episodic memory and provides a benchmark to assess the effect of MRI-LA on the clinical presentation of dementia.
authors.affiliation: Department of Neurology, Drexel University College of Medicine, Mail Stop 423, 245 North 15th St, Philadelphia, PA 19102, USA. dlibon@drexelmed.edu
authors.forename: David J
authors.initials: DJ
authors.lastname: Libon
authors.forename: Catherine C
authors.initials: CC
authors.lastname: Price
authors.forename: Tania
authors.initials: T
authors.lastname: Giovannetti
authors.forename: Rodney
authors.initials: R
authors.lastname: Swenson
authors.forename: Brianne Magouirk
authors.initials: BM
authors.lastname: Bettcher
authors.forename: Kenneth M
authors.initials: KM
authors.lastname: Heilman
authors.forename: Alfio
authors.initials: A
authors.lastname: Pennisi
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019985:Benchmarking; D015331:Cohort Studies; D003704:Dementia / Q000175:diagnosis / Q000209:etiology*; D004056:Differential Threshold; D006801:Humans; D049292:Leukoaraiosis / Q000175:diagnosis* / Q000523:psychology*; D008279:Magnetic Resonance Imaging; D008568:Memory; D009483:Neuropsychological Tests; D011569:Psychiatric Status Rating Scales; D012720:Severity of Illness Index