| Since Alzheimer's disease (AD) and vascular dementia (VaD) are associated with considerable morbidity and mortality and together comprise roughly 80% of all dementia cases worldwide (Morris, 1994; Small, Rabins, Barry, & Buckholtz, 1997), delineating and elucidating early, pre-clinical manifestations of these dementia syndromes is essential. Although no reliable treatments currently exist for dementia, it is important to identify and define early stages of the dementing process with the goal of more clearly understanding how and why dementia progresses; in addition, identifying early manifestations of dementia is important in terms of possibly staving off future cognitive decline with existing pharmacological treatment. Mild Cognitive Impairment (MCI), a reliable clinical entity that has received considerable attention since its inception in 1997, is thought to represent a vulnerable population lying between normal aging and dementia (Morris et al., 2001; Petersen et al., 2001). Indeed, understanding what constitutes MCI is imperative as several studies have indicated that individuals in this at-risk group are at dramatically increased risk for dementia and mortality (Palmer et al., 2003; Petersen et al., 1999).; This study examined whether distinct neuropsychological profiles could be delineated within an MCI population as well as to investigate the contribution of white matter lesions (WML) to associated cognitive impairment. A clinical sample of 70 older adults diagnosed with MCI (age range 55-88) was assessed using neuropsychological test scores (CERAD battery, Trails A and B, and Stroop Color Word Test). Additionally, WML found on structural MRI was measured using a semi-automated volumetric approach (Pixel Thresholding) with T2-weighted FLAIR (fluid-attenuated inversion recovery) images. Using cluster and discriminant analyses, three distinct groups (Cortical, Subcortical, and Amnestic) were formed based on neuropsychological scores. Results showed that each group differed on white matter lesion load, with the Subcortical group demonstrating the highest level of WML pathology. Finally, using regression analyses, the effect of lesion type (deep white matter (DWML) versus periventricular (PVL)) on neuropsychological performance was investigated. Only DWML was associated with greater cognitive impairment, likely due to frontal-subcortical circuitry disruption. Taken together, findings suggest that distinct neuropsychological profiles exist within MCI and that these profiles differ according to levels of WML. Clinical, theoretical, and methodological implications of these results are discussed. |
