Parkinson's disease diffusion MRI is not affected by acute antiparkinsonian medication

Objective A prior longitudinal study demonstrates that free-water diffusion magnetic resonance imaging (dMRI) tracks progression in the substantia nigra (Ofori et al., 2015b). Here, we test the acute effects of antiparkinsonian medication on this established imaging progression marker for the first time. Methods Fifteen PD patients underwent dMRI OFF and ON-medication one day apart. ON-medication, patients were tested approximately 45 min after their usual dose of antiparkinsonian medication. OFF-medication, patients were tested after not taking antiparkinsonian medication for > 12 h. OFF and ON-medication was counter-balanced across subjects. For dMRI, we computed free-water and free-water corrected fractional anisotropy (FA_t) within the following regions: caudate, putamen, substantia nigra, and subthalamic nucleus. Results ON-medication significantly reduced parkinsonian motor symptoms compared with OFF-medication (p < 0.001). dMRI measures (free-water and FA_t) were not different between the OFF and ON-medication conditions. Conclusions Administration of an acute does of anti-parkinsonian medication in PD does not affect free-water and FA_t in key nigrostriatal structures. Free-water and FA_t biomarkers reflect the chronic state of the nigrostriatal circuit, and therefore are potential viable biomarkers for disease-modifying therapeutic studies in PD.