BackgroundNeuroimaging studies help us better understand the pathophysiology and symptoms of Parkinson's disease (PD). In several of these studies, diffusion tensor imaging (DTI) was used to investigate structural changes in cerebral tissue. Although data have been provided as regards to specific brain areas, a whole brain meta-analysis is still missing.MethodsWe compiled 39 studies in this meta-analysis: 14 used fractional anisotropy (FA), 1 used mean diffusivity (MD), and 24 used both indicators. These studies comprised 1855 individuals, 1087 with PD and 768 healthy controls. Regions of interest were classified anatomically (subcortical structures; white matter; cortical areas; cerebellum). Our statistical analysis considered the disease effect size (DES) as the main variable; the heterogeneity index (I2) and Pearson's correlations between the DES and co-variables (demographic, clinical and MRI parameters) were also calculated.ResultsOur results showed that FA-DES and MD-DES were able to distinguish between patients and healthy controls. Significant differences, indicating degenerations, were observed within the substantia nigra, the corpus callosum, and the cingulate and temporal cortices. Moreover, some findings (particularly in the corticospinal tract) suggested opposite brain changes associated with PD. In addition, our results demonstrated that MD-DES was particularly sensitive to clinical and MRI parameters, such as the number of DTI directions and the echo time within white matter.ConclusionsDespite some limitations, DTI appears as a sensitive method to study PD pathophysiology and severity. The association of DTI with other MRI methods should also be considered and could benefit the study of brain degenerations in PD.

Parkinson's disease (PD) results from neurodegenerative processes leading to alteration of motor functions. Most motor symptoms respond well to pharmacological and neurosurgical treatments, except some axial symptoms such as speech impairment, so-called dysarthria. However, speech therapy is rarely proposed to PD patients. This review aims at evaluating previous research on the effects of speech behavioral therapies in patients with PD. We also performed two meta-analyses focusing on speech loudness and voice pitch. We showed that intensive therapies in PD are the most effective for hypophonia and can lead to some improvement of voice pitch. Although speech therapy is effective in handling PD dysarthria, behavioral speech rehabilitation in PD still needs further validation.