Diffusion imaging of nigral alterations in early Parkinson's disease with dopaminergic deficits.

BACKGROUND: This study reports the baseline characteristics of diffusion tensor imaging data in Parkinson's disease (PD) patients and healthy control subjects from the Parkinson's Progression Markers Initiative. The main goals were to replicate previous findings of abnormal diffusion imaging values from the substantia nigra. in a large multicenter cohort and determine whether nigral diffusion alterations are associated with dopamine deficits. METHODS: Two hundred twenty subjects (PD = 153; control = 67) from 10 imaging sites were included. All subjects had a full neurological exam, a ((123) I)ioflupane dopamine transporter (DAT) single-photon emission computer tomography scan, and diffusion tensor imaging. Fractional anisotropy as well as radial and axial diffusivity was computed within multiple regions across the substantia nigra. RESULTS: A repeated-measures analysis of variance found a marginally nonsignificant interaction between regional fractional anisotropy of the substantia nigra and disease status (P = 0.08), conflicting with an earlier study. However, a linear mixed model that included control regions in addition to the nigral regions revealed a significant interaction between regions and disease status (P = 0.002), implying a characteristic distribution of reduced fractional anisotropy across the substantia nigra in PD. Reduced fractional anisotropy in PD was also associated with diminished DAT binding ratios. Both axial and radial diffusivity were also abnormal in PD. CONCLUSIONS: Although routine nigral measurements of fractional anisotropy are clinically not helpful, the findings in this study suggest that more-sophisticated diffusion imaging protocols should be used when exploring the clinical utility of this imaging modality.

Diffusion tensor imaging of the nigrostriatal fibers in Parkinson's disease.

BACKGROUND: Parkinson's disease (PD) is histopathologically characterized by the loss of dopamine neurons in the substantia nigra pars compacta. The depletion of these neurons is thought to reduce the dopaminergic function of the nigrostriatal pathway, as well as the neural fibers that link the substantia nigra to the striatum (putamen and caudate), causing a dysregulation in striatal activity that ultimately leads to lack of movement control. Based on diffusion tensor imaging, visualizing this pathway and measuring alterations of the fiber integrity remain challenging. The objectives were to 1) develop a diffusion tensor tractography protocol for reliably tracking the nigrostriatal fibers on multicenter data; 2) test whether the integrities measured by diffusion tensor imaging of the nigrostriatal fibers are abnormal in PD; and 3) test whether abnormal integrities of the nigrostriatal fibers in PD patients are associated with the severity of motor disability and putaminal dopamine binding ratios. METHODS: Diffusion tensor tractography was performed on 50 drug-naïve PD patients and 27 healthy control subjects from the international multicenter Parkinson's Progression Marker Initiative. RESULTS: Tractography consistently detected the nigrostriatal fibers, yielding reliable diffusion measures. Fractional anisotropy, along with radial and axial diffusivity of the nigrostriatal tract, showed systematic abnormalities in patients. In addition, variations in fractional anisotropy and radial diffusivity of the nigrostriatal tract were associated with the degree of motor deficits in PD patients. CONCLUSION: Taken together, the findings imply that the diffusion tensor imaging characteristic of the nigrostriatal tract is potentially an index for detecting and staging of early PD.

Plasma apolipoprotein A1 as a biomarker for Parkinson disease.

OBJECTIVE: To identify plasma-based biomarkers for Parkinson disease (PD) risk. METHODS: In a discovery cohort of 152 PD patients, plasma levels of 96 proteins were measured by multiplex immunoassay; proteins associated with age at PD onset were identified by linear regression. Findings from discovery screening were then assessed in a second cohort of 187 PD patients, using a different technique. Finally, in a third cohort of at-risk, asymptomatic individuals enrolled in the Parkinson's Associated Risk Study (PARS, n = 134), plasma levels of the top candidate biomarker were measured, and dopamine transporter (DAT) imaging was performed, to evaluate the association of plasma protein levels with dopaminergic system integrity. RESULTS: One of the best candidate protein biomarkers to emerge from discovery screening was apolipoprotein A1 (ApoA1; p = 0.001). Low levels of ApoA1 correlated with earlier PD onset, with a 26% decrease in risk of developing PD associated with each tertile increase in ApoA1 (Cox proportional hazards, p < 0.001, hazard ratio = 0.742). The association between plasma ApoA1 levels and age at PD onset was replicated in an independent cohort of PD patients (p < 0.001). Finally, in the PARS cohort of high-risk, asymptomatic subjects, lower plasma levels of ApoA1 were associated with greater putaminal DAT deficit (p = 0.037). INTERPRETATION: Lower ApoA1 levels correlate with dopaminergic system vulnerability in symptomatic PD patients and in asymptomatic individuals with physiological reductions in dopamine transporter density consistent with prodromal PD. Plasma ApoA1 may be a new biomarker for PD risk.