Background: The semantic variant of primary progressive aphasia (svPPA) is a form of dementia, mainly featuring language impairment, for which the extent of white matter (WM) damage is less described than its associated grey matter (GM) atrophy. Our study aimed to characterise the extent of this damage using a sensitive and unbiased approach. Methods: We conducted a between-group study comparing 10 patients with a clinical diagnosis of svPPA, recruited between 2011 and 2014 at a tertiary reference centre, with 9 cognitively healthy, age-matched controls. From diffusion tensor imaging (DTI) data, we extracted fractional anisotropy (FA) values using a tract-based spatial statistics approach. We further obtained GM volumetric data using the Freesurfer automated segmentation tool. We compared both groups using non-parametric Wilcoxon rank-sum tests, correcting for multiple comparisons. Results: Demographic data showed that patients and controls were comparable. As expected, clinical data showed lower results in svPPA than controls on cognitive screening tests. Tractography showed impaired diffusion in svPPA patients, with FA mostly decreased in the longitudinal, uncinate, cingulum and external capsule fasciculi. Volumetric data show significant atrophy in svPPA patients, mostly in the left entorhinal, amygdala, inferior temporal, middle temporal, superior temporal and temporal pole cortices, and bilateral fusiform gyri. Conclusions: This syndrome appears to be associated not only with GM but also significant WM degeneration. Thus, DTI could play a role in the differential diagnosis of atypical dementia by specifying WM damage specific to svPPA.

Background: Differentiating Alzheimer's disease (AD) and dementia with Lewy bodies (DLB), two of the commonest forms of dementia in older age, remains a diagnostic challenge. To assist with better understanding of the differences between the conditions during life, we assessed limbic and subcortical brain volumes in AD, DLB, and healthy older individuals using magnetic resonance imaging (MRI), with the hypothesis that when compared with controls, subcortical volumes would be reduced to a greater extent in DLB than in AD.

Methods: One hundred participants (35 healthy controls, 32 AD, and 33 DLB) underwent 3 Tesla T1 weighted MR scanning. Volumes were automatically segmented for each participant using FreeSurfer, then expressed as a percentage of their total intracranial volumes. Group effects were assessed using multivariate analysis of covariance, controlling for age and gender.

Results: Significant group effects were apparent among subcortical brain volumes (F28,162 = 4.8, p < 0.001; Wilk's Λ = 0.30, partial η2 = 0.45), while univariate tests showed differences in all volumetric measures (p < 0.03) except in right caudate (p = 0.08). Post-hoc analyses indicated that while not significantly different from AD, changes compared to healthy subjects in left caudate, bilateral putamen, left thalamus, brainstem and total subcortical grey volume were more pronounced in DLB. Significant differences between AD and DLB were confined to the bilateral hippocampus (DLB > AD, p < 0.008).

Conclusions: For similar levels of dementia severity, DLB appears to have greater involvement of subcortical brain atrophy than AD. Further investigation of the subcortical brain structures in DLB is warranted to fully understand their neurobiological role in this disease.