Optic nerve integrity as a visuospatial cognitive predictor in Parkinson's disease

Objective: To explore the microstructural integrity of the optic nerve and its role as a cognitive predictor in patients with de novo Parkinson's disease (PD) using diffusion tensor image-based magnetic resonance scans. Methods: We enrolled 82 patients with de novo PD, 36 patients with drug-induced parkinsonism (DIP), and 36 controls. Fractional anisotropy (FA) and apparent diffusion coefficient (ADC) were measured on the mid-portion of the intraorbital optic nerve. Using a multivariate analysis of variance with repeated measures, longitudinal changes in cognitive subscores of a comprehensive neuropsychological test were evaluated in PD patients according to optic nerve integrity. Results: The mean FA value in PD was significantly lower (0.552 0.103, p < 0.001) than that in DIP (0.645 +/- 0.099) or the controls (0.689 +/- 0.089), whereas the mean ADC value was significantly higher in the PD group compared to the DIP or control group (p < 0.001). Optic nerve integrity was not associated with parkinsonian motor severity, striatal dopamine transporter activity, olfaction, or baseline cognitive performance in PD patents. In a longitudinal assessment of cognition in PD, the lower FA group showed significant decline in the performance of Clock Drawing Test (F = 3.39, p = 0.038), but no significant differences in the other cognitive subsets. Conclusion: This study demonstrated that microstructural integrity in the optic nerve was distorted in PD patients, and that this nerve integrity might act as a cognitive predictor of visuospatial dysfunction. (C) 2016 Published by Elsevier Ltd.