These results show that DWI detects basal ganglia abnormalities in PSP patients within few years of disease onset, discriminating patients with PSP from those with PD, but not from those with MSA-P.

DWI, even if measured in the slice direction only, is able to discriminate MSA-P and both patients with PD and healthy volunteers on the basis of putaminal rADC values. The increased putaminal rADC values in Parkinson variant of multiple system atrophy are likely to reflect ongoing striatal degeneration, whereas most neuropathologic studies reveal intact striatum in PD. Diffusion-weighted imaging may represent a useful diagnostic tool that can provide additional support for a diagnosis of Parkinson variant of multiple system atrophy.

Visual assessment of dorsolateral nigral hyperintensity on high-field SWI scans may serve as a new simple diagnostic imaging marker for neurodegenerative parkinsonian disorders.

The differential diagnosis of parkinsonian syndromes is considered one of the most challenging in neurology, even for movement disorder specialists. Despite published consensus operational criteria for the diagnosis of Parkinson’s disease (PD) and the various atypical parkinsonian disorders (APDs) such as progressive supranuclear palsy, multiple system atrophy, and corticobasal syndrome, the clinical separation of APDs from PD carries a high rate of misdiagnosis. However, an early differentiation between APD and PD, each characterized by a largely different natural history, is crucial for determining the prognosis and choosing a treatment strategy. Despite limitations, the different modern magnetic resonance (MR) techniques have undoubtedly added to the differential diagnosis of neurodegenerative parkinsonism. Conventional MRI with visual assessment of T₂- and T₁-weighted imaging as well as various advanced MRI techniques offer objective measures and may therefore be useful tools in the diagnostic workup of PD and APDs. In clinical practice, conventional MRI is a well-established method for the exclusion of symptomatic parkinsonism due to other pathologies such as tumors, cerebral ischemia or inflammatory diseases. Furthermore, over the past two decades, advances in MR techniques have enabled to quantitatively illustrate abnormalities in the basal ganglia and infratentorial structures in APDs by methods such as magnetic resonance volumetry, diffusion-weighted imaging, magnetization transfer imaging and proton magnetic resonance spectroscopy. This article aims to review research findings on the value of MRI techniques in the differential diagnosis of neurodegenerative parkinsonian disorders.

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Using magnetic resonance (MR) planimetry, both the midbrain-to-pontine area ratio (m/p-ratio) and the MR parkinsonism index (MRPI) have been shown to assist in the differential diagnosis of progressive supranuclear palsy (PSP) from Parkinson's disease (PD) and the Parkinson variant of multiple system atrophy (MSA-P). The aim of this study was to determine the diagnostic accuracy of the MRPI compared with the m/p-ratio in a large cohort of 123 patients with neurodegenerative parkinsonism including patients with PSP, PD, and MSA-P. Patients with PSP had significant higher MRPI values and significant smaller m/p-ratios compared with the other groups with overlapping individual values. Overall predictive accuracy was similar for the m/p-ratio (87.0%) and the MRPI (80.5%) with a predictive accuracy for PSP from MSA-P being significantly better for the MRPI (87.5%) compared with the m/p-ratio (75%) as well as a predictive accuracy for PSP from PD being significantly better for the m/p-ratio (87.6%) compared with the MRPI (77.3%). Both the m/p-ratio and the MRPI may assist the clinical differential diagnosis in neurodegenerative parkinsonism.

We were able to demonstrate that brainstem-derived MR planimetric measures yield high diagnostic accuracy for the discrimination of PSP from related disorders when decision tree algorithms are applied, even at early, clinically uncertain stages. However, their diagnostic accuracy in discriminating PD and MSA was suboptimal.