Longitudinal Changes in the Digitized Archimedes Spiral Drawing Test Following iTBS of the Left DLPFC in Parkinson's Disease: An Exploratory Feasibility Study.

Background: The Digitized Archimedes Spiral Drawing Test (DAST) provides objective assessment of fine motor function, but its utility as a biomarker for neuromodulatory interventions in Parkinson's disease (PD) remains underexplored. Objective: To explore longitudinal changes in a comprehensive set of DAST parameters following a course of intermittent theta-burst stimulation (iTBS) of the left dorsolateral prefrontal cortex (DLPFC) in PD patients as a feasibility study. Methods: Twenty-seven participants (17 PD patients, 10 healthy controls) underwent DAST testing at baseline and at 1.5 and 6 months; the immediate post-course assessment was performed only in the PD group, whereas the controls received a single sham session. Forty kinematic, temporal, spatial and tremor-related metrics were extracted. Clinical assessment was performed using MDS-UPDRS. Linear mixed models, ANCOVA, and Friedman tests were applied for statistical analysis. Results: Temporal and kinematic parameters showed modest changes over the study period, including mean velocity (p = 0.0437), trial duration (p = 0.0437), and mean number of movements (p = 0.0485). In contrast, spatial parameters (total error and length-normalized error) showed no significant change over the study period but maintained stable between-group differences across all stages (p = 0.0251 and p = 0.0123 at 6 months). Age and sex significantly influenced several DAST metrics: age affected mean error for spiral types 2, 3, and 4 (p = 0.008-0.047), while sex influenced dominant tremor frequency, tremor power ratio (p = 0.005-0.007), and mean error for spiral types 3 and 4 (p = 0.023-0.039). The DAST showed limited ability to differentiate adjacent PD stages: only mean velocity of spiral type 2 differed between Hoehn and Yahr stages 2 and 3 at baseline (p = 0.0176), with no significant differences between subgroups at 6 months. Conclusions: The changes over the study period were observed in kinematic and temporal DAST measures, but not in spatial parameters. These preliminary findings may suggest a possible dissociation between parameters predominantly reflecting motor planning and those reflecting trajectory execution. It may be tentatively hypothesized that DLPFC stimulation primarily modulates motor planning processes and movement execution strategies, whereas trajectory implementation and spatial coordination appear to be mediated by other cortico-subcortical structures. DAST shows potential as an objective tool for monitoring motor changes in PD; nevertheless, its responsiveness should be further evaluated in larger studies.