Apparent diffusion coefficient of the superior cerebellar peduncle differentiates progressive supranuclear palsy from Parkinson's disease.

The early diagnosis of progressive supranuclear palsy (PSP) may be challenging, because of clinical overlapping features with Parkinson's disease (PD) and other parkinsonian syndromes such as the Parkinsonian variant of multiple system atrophy (MSA-P). Conventional MRI can help in differentiating parkinsonian disorders but its diagnostic accuracy is still unsatisfactory. On the basis of the pathological demonstration of superior cerebellar peduncle (SCP) atrophy in patients with PSP, we assessed the SCP apparent diffusion coefficient (ADC) values in patients with PSP, PD, and MSA-P in order to evaluate its differential diagnostic value in vivo. Twenty-eight patients with PSP (14 with possible- PSP and 14 with probable-PSP), 15 PD, 15 MSA-P, and 16 healthy subjects were studied by using diffusion weighted imaging (DWI). ADC was calculated in regions of interest defined in the left and right SCP by two clinically blinded operators. Intrarater (r 5 0.98, P < 0.001) and interrater reliability (r 5 0.97; P < 0.001) for SCP measurements were high. Patients with PSP had higher SCP rADC values (median 0.98 3 1023mm2/s) than patients with PD (median 0.79 3 1023 mm2/s, P < 0.001), MSA-P (median 0.79 3 1023 mm2/s, P < 0.001), and healthy controls (median 0.80 3 1023 mm2/s, P < 0.001). DWI discriminated patients with PSP from PD and healthy subjects on the basis of SCP rADC individual values (100% sensitivity and specificity) and from patients with MSA-P (96.4% sensitivity and 93.3% specificity). The higher values of rADC in SCP of patients with PSP correspond with the in vivo microstructural feature of atrophy detected postmortem and provide an additional support for early discrimination between PSP and other neurodegenerative parkinsonisms.