Ultrasound Characteristics of the Substantia Nigra in Parkinson's Disease Patients With Different Motor Subtypes.

This research aims to analyze ultrasound characteristics of substantia nigra (SN) in Parkinson's disease (PD) patients with distinct motor subtypes and to identify factors influencing positive SN hyperechogenicity. We retrospectively analyzed 196 PD patients. Based on the motor subtypes of the Unified Parkinson's Disease Rating Scale (UPDRS III), patients were classified into tremor-dominant (TD; n = 62) and postural instability/gait difficulty (PIGD; n = 134) subtypes. Based on SN hyperechogenicity status, patients were dichotomized into negative SN hyperechogenicity (n = 39) and positive SN hyperechogenicity (n = 157) groups. PIGD patients showed a larger SN hyperechogenic area, higher S/M ratio, and greater positivity rates. PIGD+ patients had the highest TCS metrics across subgroups. Motor subtypes correlated positively with all TCS indices. Logistic regression revealed smoking, constipation, PIGD subtype, older age, and longer disease duration as independent risk factors, while higher serum uric acid was associated with positivity. Higher serum uric acid was a protective factor. The resulting nomogram indicated excellent calibration and discrimination based on readily available clinical data, offering practical utility for identifying patients at higher risk of SN hyperechogenicity in PD. Moreover, by linking clinical motor phenotypes with nigral echogenic alterations, these findings consolidate existing evidence, provide mechanism-informed support for disease heterogeneity, and translate such insights into a clinically applicable prediction tool.