Quantitative analysis of striatal subregional asymmetry on 99mTc-TRODAT-1 SPECT and clinical correlations with UPDRS subscales in Parkinson's disease.

Objective: To investigate the relationship between striatal asymmetry indices-namely the High/Low Ratio and Asymmetry Index (AI)-derived from dopamine transporter single-photon emission computed tomography (DAT-SPECT) using ^99mTc-TRODAT-1, and the subscale scores of the Unified Parkinson's Disease Rating Scale (UPDRS), with the aim of evaluating their utility in clinical phenotyping and symptom assessment in Parkinson's disease (PD).

Methods: Fifty-six patients with clinically diagnosed PD underwent ^99mTc-TRODAT-1 SPECT imaging and UPDRS evaluation. Radiotracer uptake in the caudate nucleus, putamen, and whole striatum was quantified bilaterally, and corresponding High/Low Ratios and AIs were calculated. These asymmetry measures were analyzed in relation to UPDRS subscale scores and Hoehn-Yahr stages.

Results: Putaminal asymmetry was significantly greater in early-stage PD patients (Hoehn-Yahr ≤ 2; p = 0.010), suggesting early lateralized dopaminergic degeneration. The AI of the caudate nucleus was strongly correlated with UPDRS Part I (non-motor symptoms; r = 0.690, p < 0.001), while putaminal asymmetry was significantly associated with UPDRS Part III (motor symptoms; r = 0.497, p < 0.001).

Conclusion: Region-specific DAT-SPECT asymmetry shows domain-specific correlations in PD (caudate-non-motor; putamen-motor). These findings may support the use of TRODAT-1-based imaging biomarkers for precision assessment and individualized management; however, they are hypothesis-generating and require confirmation in larger, better-balanced prospective cohorts.