White matter microstructural changes in pure Alzheimer’s disease and subcortical vascular dementia Y. J. Kim a,b , H. K. Kwon c , J.-M. Lee c , Y. J. Kim d , H. J. Kim a,b , N.-Y. Jung a,b , S. T. Kim e , K. H. Lee f , D. L. Na a,b and S. W. Seo a,b a Department of Neurology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul; b Neuroscience Center, Samsung Medical Center, Seoul; c Department of Biomedical Engineering, Hanyang University, Seoul; d Department of Neurology, Ilsong Institute of Life Science, Hallym University, Anyang; e Radiology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul; and f Nuclear Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea Keywords: Alzheimer’s disease, diffuse tensor imaging, subcortical vascular dementia, white matter microstructural changes Received 11 September 2014 Accepted 12 November 2014 European Journal of Neurology 2015, 22: 709–716 doi:10.1111/ene.12645 Background and purpose: Recent studies have demonstrated that Alzheimer’s disease (AD) and subcortical vascular dementia (SVaD) have white matter (WM) microstructural changes. However, previous studies on AD and SVaD rarely eliminated the confounding effects of patients with mixed Alzheimer’s and cerebrovascular disease pathologies. Therefore, our aim was to evaluate the divergent topography of WM microstructural changes in patients with pure AD and SVaD. Methods: Patients who were clinically diagnosed with AD and SVaD were prospectively recruited. Forty AD patients who were Pittsburgh compound B (PiB) positive [PiB(+) AD] without WM hyperintensities and 32 SVaD patients who were PiB negative [PiB(À) SVaD] were chosen. Fifty-six cognitively nor- mal individuals were also recruited (NC). Tract-based spatial statistics of dif- fuse tensor imaging were used to compare patterns of fractional anisotropy (FA) and mean diffusivity (MD). Results: Compared with the NC group, the PiB(+) AD group showed decreased FA in the bilateral frontal, temporal and parietal WM regions and the genu and splenium of the corpus callosum as well as increased MD in the left frontal and temporal WM region. PiB(À) SVaD patients showed decreased FA and increased MD in all WM regions. Direct comparison between PiB(+) AD and PiB(À) SVaD groups showed that the PiB(À) SVaD group had decreased FA across all WM regions and increased MD in all WM regions except occipital regions. Conclusion: Our findings suggest that pure AD and pure SVaD have diver- gent topography of WM microstructural changes including normal appearing WM. Introduction Alzheimer’s disease (AD) and subcortical vascular dementia (SVaD) are the two most common causes of dementia. AD is characterized by accumulation of amyloid plaques and neurofibrillary tangles in the cortex, which in turn lead to cortical atrophy [1]. SVaD is characterized by ischaemic changes in the white matter (WM) or deep nuclei caused by small vessel disease [2]. Clinically, AD patients have more impaired episodic memory function whilst SVaD patients have more impaired frontal/executive func- tion [3]. However, pathological studies have suggested that patients clinically diagnosed with SVaD have co-associated AD pathology and vice versa [4,5]. With the advent of diffusion tensor imaging (DTI), which is a sensitive tool for detecting microstructural Correspondence: Sang Won Seo, MD, PhD, Department of Neurology, Sungkyunkwan University School of Medicine, Samsung Medical Center, 50 Ilwon-dong, Gangnam-gu, Seoul 135-710, Korea (tel.: +82 2 3410 1233; fax: +82 2 3410 0052; e-mail: sangwonseo@empal.com). © 2015 EAN 709 ORIGINALARTICLE EUROPEANJOURNALOFNEUROLOGY