LAUSR

Despite the continuous refining of clinical criteria and consensus statements, the differential diagnosis between idiopathic Parkinson’s disease (PD) and atypical parkinsonian syndromes (APS), particularly at the early stages of these conditions, remains challenging even in specialized Movement Disorder Clinics. An early and more accurate diagnosis of APS would benefit the affected patients, because they could receive from the very beginning a more focused and disease-specific management, including the multidisciplinary approach required for these conditions. The identification of early biomarkers of neurodegenerative parkinsonisms could also facilitate the development of therapeutic strategies for these conditions, which is currently hampered by the low initial diagnostic accuracy of APS and the lack of sensitive and objective biomarkers of disease progression for both APS and PD. Magnetic resonance imaging with conventional sequences (cMRI) is the most widely available neuroimaging technique in clinical settings. Although no significant abnormalities are generally detected in patients with idiopathic PD on cMRI images, a number of characteristic features have been reported in patients with APS, particularly in those with established and more advanced diseases. The presence of these cMRI abnormalities can support the diagnosis of a specific condition, but unfortunately, an overlap among these conditions often exists, reducing the effective diagnostic value of these findings. Additionally, the effect size of these features in differentiating parkinsonian disorders has not been fully investigated. Dr. Lee from Box Hill Hospital, Australia, has performed a meta-analysis to quantify the effect size of the most common cMRI features that have been reported to differentiate parkinsonian disorders with statistical significance. Thirty-six papers assessing cMRI findings in at least 2 Parkinsonian disorders, including PD, were included in the analysis that demonstrated a large effect size in differentiating parkinsonian disorders for the presence but not the absence of some characteristic cMRI features (putaminal, pontine, and middle cerebellar peduncle abnormalities for multiple system atrophy; reduced midbrain and superior cerebellar peduncle diameters for progressive supranuclear palsy). Overall, cMRI showed limited use in patients with high pretest probability but, importantly, it was more useful in patients with low to moderate pretest probability. Taken together, the results of this meta-analysis confirm that cMRI features are not decisive but can be useful for the diagnosis of APS, although they should always be considered in conjunction with the clinical presentation. More sophisticated MRI sequences are now available to visualize substantia nigra pathology in vivo, and a number of published papers with promising findings indicate that these techniques could also provide higher sensitivity and specificity to differentiate PD from APS. However, further research is required to confirm these initial findings in larger cohorts of patients and to assess the real use of these MRI techniques in clinical practice. Kathuria and colleagues have used 3T MRI with venous blood oxygen level-dependent (VenoBOLD) and high-resolution susceptibility-weighted imaging (SWI) sequences to investigate the use of nigrosome imaging in the diagnosis of idiopathic PD and APS. In line with previous studies, they found that loss of nigrosome-1 on MRI images can be useful in the diagnosis of idiopathic PD. The diagnostic sensitivity and specificity of the detection of loss of nigrosome-1 appear to be higher with SWI sequences than VenoBOLD sequences (94% and 80% vs. 90% and 66.7%, respectively). Conversely, the loss of nigrosome-1 on both SWI and VenoBOLD sequences did not