Objective: To assess whether microstructural integrity of the posterior limb of the internal capsule, measured by diffusion MRI fractional anisotropy, is associated with motor outcome after functional neurosurgical treatment in Parkinson’s disease.

Background: Motor outcomes following functional neurosurgical treatment in Parkinson’s disease (PD) vary substantially across patients. Microstructural integrity of corticospinal pathways may contribute to differences in motor responsiveness and may reflect motor reserve.

Method: We evaluated 98 patients with PD undergoing functional neurosurgical treatment with 18-month follow-up, including deep brain stimulation (DBS, n=49) and radiofrequency lesioning (RF, n=49). Mean age was 64.8 ± 7.9 years and mean disease duration was 11.3 ± 3.8 years. Baseline motor severity averaged UPDRS-III 50.3 ± 11.4. Diffusion MRI metrics were obtained bilaterally from the posterior limb of the internal capsule (PLIC), and mean fractional anisotropy (FA) values were calculated. Clinical characterization included baseline cognition and motor phenotype.

Results: UPDRS-III improved from 50.3 ± 11.4 at baseline to 33.7 ± 10.2 at 18 months, corresponding to a mean improvement of 16.7 ± 8.9 points. Patients with greater motor improvement showed higher mean PLIC FA than those with lower motor response (0.6253 ± 0.011 vs 0.6204 ± 0.012, p<0.05). Similar directional differences were observed bilaterally in the right PLIC (0.626 ± 0.012 vs 0.621 ± 0.013) and left PLIC (0.624 ± 0.011 vs 0.620 ± 0.012). PLIC asymmetry remained low overall (0.0188 ± 0.006). FA distributions were comparable between DBS and RF groups.

Conclusion: Corticospinal FA and baseline clinical characteristics demonstrated complementary associations with motor improvement. These findings suggest that corticospinal microstructural integrity may reflect motor reserve and may contribute to individualized prognostic assessment in surgical candidates.

Table 1

References: • Loehrer PA, Freigang J, Bopp MHA, et al. Microstructure is associated with motor outcomes following Deep Brain Stimulation in Parkinson’s disease. NPJ Parkinsons Dis. 2025;11(1):81. doi: 10.1038/s41531-025-00930-3
• Fu Y, Zhou L, Li H, et al. Adaptive structural changes in the motor cortex and white matter in Parkinson’s disease. Acta Neuropathol. 2022;144(5):861-879. doi: 10.1007/s00401-022-02488-3.
• Prasad S, Nagaraj T, Bhat SGS, et al. White matter alterations in tremor-dominant and postural instability and gait disturbance subtypes of Parkinson’s disease. J Neural Transm (Vienna). 2026;133(1):87-98. doi: 10.1007/s00702-025-03001-2.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/plic-fractional-anisotropy-and-motor-outcome-after-functional-neurosurgical-treatment-in-parkinsons-disease/