Visual Hallucinations (VH) are among the core features of Dementia with Lewy Bodies (DLB), but are also very frequent in demented patients with Parkinson's Disease (PDD). The purpose of this study was to investigate the pattern of gray matter and cognitive impairment underlying VH in DLB and PDD. We applied voxel-based morphometry and behavioral assessment to 12 clinically diagnosed DLB patients and 15 PDD patients. Subjects with VH showed greater gray matter loss than non-hallucinators, specifically in the right inferior frontal gyrus (BA 45) in the DLB patients and in the left orbitofrontal lobe (BA 10) in the PDD patients. Comparing the two subgroups with VH, DLB patients had greater decrease of the bilateral premotor area (BA 6) than PDD patients. Furthermore, decreased volume in associative visual areas, namely left precuneus and inferior frontal lobe, correlated with VH in the DLB but not in PDD patients. VH were related to impaired verbal fluency, inhibitory control of attention and visuoperception in the DLB group and to visual memory in the PDD group. In conclusion, DLB and PDD patients with VH had more frontal gray matter atrophy than non-hallucinators, the impairment being greater in the DLB group. The patterns of structural and functional correlations were different in both pathologies.

Neurodegeneration of the striatum in Huntington disease (HD) is characterized by loss of medium-spiny neurons, huntingtin nuclear inclusions, reactive gliosis, and iron accumulation. Neuroimaging allows in vivo detection of the macro- and micro-structural changes that occur from presymptomatic stages of the disease (preHD). The aim of our study was to evaluate the reliability of multimodal imaging as an in vivo biomarker of vulnerability and development of the disease and to characterize macro- and micro-structural changes in subcortical nuclei in HD. Macrostructure (T1-weighted images), microstructure (diffusion tensor imaging), and iron content (R 2* relaxometry) of subcortical nuclei and medial temporal lobe structures were evaluated by a 3 T scanner in 17 preHD carriers, 12 early-stage patients and 29 matched controls. We observed a volume reduction and microstructural changes in the basal ganglia (caudate, putamen, and globus pallidus) and iron accumulation in the globus pallidus in both preHD and symptomatic subjects; all these features were significantly more pronounced in patients, in whom degeneration extended to the other subcortical nuclei (i.e., thalamus and accumbens). Mean diffusivity (MD) was the most powerful predictor in models explaining more than 50% of the variability in HD development in the caudate, putamen, and thalamus. These findings suggest that the measurement of MD may further enhance the well-known predictive value of striatal volume to assess disease progression as it is highly sensitive to tissue microimpairment. Multimodal imaging may detect brain changes even in preHD stages.

Recent magnetic resonance imaging (MRI) studies suggest that abnormalities in Huntington's disease (HD) extend to white matter (WM) tracts in early HD and even in presymptomatic stages. Thus, changes of the corpus callosum (CC) may reflect various aspects of HD pathogenesis. We recruited 17 HD patients, 17 pre-HD subjects, and 34 healthy age-matched controls. Three-dimensional anatomical MRI and diffusion tensor images of the brain were acquired on a 3T scanner. Combining region-of-interest analyses, voxel-based morphometry, and tract-based spatial statistics, we investigated callosal thickness, WM density, fractional anisotropy, and radial and axial diffusivities. Compared with controls, pre-HD subjects showed reductions of the isthmus, likely due to myelin damage. Compared with pre-HD subjects, HD patients showed reductions of isthmus and body, with axonal damage confined to the body. Compared with controls, HD patients had significantly decreased callosal measures in extended regions across almost the entire CC. At this disease stage, both myelin and axonal damage are detectable. Supplementary multiple regression analyses revealed that WM reduction density in the isthmus as well as Disease Burden scores allowed to predict the "HD development" index. While callosal changes seem to proceed in a posterior-to-anterior direction as the diseases progresses, this observation requires validation in future longitudinal investigations.