Regional Selectivity of Neuromelanin Changes in the Substantia Nigra in Atypical Parkinsonism

Abstract

Background Neurodegeneration in the substantia nigra pars compacta (SNc) in parkinsonian syndromes may affect the nigral territories differently. Objective The objective of this study was to investigate the regional selectivity of neurodegenerative changes in the SNc in patients with Parkinson's disease (PD) and atypical parkinsonism using neuromelanin‐sensitive magnetic resonance imaging (MRI). Methods A total of 22 healthy controls (HC), 38 patients with PD, 22 patients with progressive supranuclear palsy (PSP), 20 patients with multiple system atrophy (MSA, 13 with the parkinsonian variant, 7 with the cerebellar variant), 7 patients with dementia with Lewy body (DLB), and 4 patients with corticobasal syndrome were analyzed. volume and signal‐to‐noise ratio (SNR) values of the SNc were derived from neuromelanin‐sensitive MRI in the whole SNc. Analysis of signal changes was performed in the sensorimotor, associative, and limbic territories of the SNc. Results SNc volume and corrected volume were significantly reduced in PD, PSP, and MSA versus HC. Patients with PSP had lower volume, corrected volume, SNR, and contrast‐to‐noise ratio than HC and patients with PD and MSA. Patients with PSP had greater SNR reduction in the associative region than HC and patients with PD and MSA. Patients with PD had reduced SNR in the sensorimotor territory, unlike patients with PSP. Patients with MSA did not differ from patients with PD. Conclusions This study provides the first MRI comparison of the topography of neuromelanin changes in parkinsonism. The spatial pattern of changes differed between PSP and synucleinopathies. These nigral topographical differences are consistent with the topography of the extranigral involvement in parkinsonian syndromes. © 2022 International Parkinson and Movement Disorder Society.

NigraNet: An automatic framework to assess nigral neuromelanin content in early Parkinson’s disease using convolutional neural network

“…normalized signal intensity (NSI) and contrast-to-noise ratio (CNR) were calculated by dividing the mean signal in the SNc by the background ROI signal. In order to correct for slice-to-slice intensity variations in the 2D TSE acquisition, and for putting the SNc signal measurements on a scale that is comparable across participants and over time, we computed normalized signal intensity (NSI) and contrast-to-noise ratio (CNR) for each slice normalizing the mean signal in SNc relative to the background signal using the following formulas ( Chougar et al, 2022 , Gaurav et al, 2021 ). …”

Magnetic resonance imaging modalities aid in the differential diagnosis of atypical parkinsonian syndromes

“…These ratios can be calculated using template-based or manually segmented SN volumes on NM images. Using both methods, the SN volume and corrected SN volume (divided by the total intracranial volume) were found to be significantly reduced in patients with PD, PSP, and MSA compared with controls, most prominently in the PSP group ( 32 ). The quantitative analyses showed reduced SNR and CNR in the PSP group compared with controls, but no significant difference between controls and the PD and MSA groups.…”

Clinical and neuroimaging features of the progressive supranuclear palsy- corticobasal degeneration continuum

“…However, iron measurements do not outperform brainstem MRI measures [24]. Neuromelanin-sensitive MRI shows reduced volume and signal in the substantia nigra in PSP compared with Parkinson's disease, and reduced volume in CBS [25 ▪ ]. FDG-PET metabolism in the substantia nigra is also abnormal in PSP, although metabolism is comparable to PD and MSA [26].…”