Differentiating tremor-dominant parkinson’s disease from essential tremor using neuromelanin- sensitive imaging and T1w/T2w ratio

Parkinson's disease (PD) and essential tremor (ET) are the most common movement disorders and share tremor symptom. This study aimed to differentiate tremor-dominant PD (TD-PD) from ET using neuromelanin-sensitive MRI (NM-MRI) and T1w/T2w ratio. We included 117 TD-PD, 43 ET with resting tremor (r-ET), 94 ET without resting tremor (nr-ET) patients, and 81 healthy controls (HC). Contrast-to-noise ratios (CNR) in the locus coeruleus (LC) and substantia nigra (SN) were calculated from NM-MRI, while T1w/T2w ratios were derived from T1- and T2-weighted images in PD- and ET-related pathological regions. TD-PD patients exhibited significantly lower CNR values in the LC and bilateral SN compared to the other three groups (all p < 0.05), with the r-ET group showing intermediate values between TD-PD and nr-ET. All patient groups demonstrated higher T1w/T2w ratio compared to HC (p < 0.05), following a consistent pattern of TD-PD > r-ET > nr-ET across most regions of basal ganglia and cerebellar structures. Combining NM-MRI with T1w/T2w ratio analysis improved differentiation efficiency, with AUCs of 0.798 (TD-PD vs r-ET) and 0.851 (TD-PD vs nr-ET). The intermediate imaging profile of r-ET suggests a potential pathophysiological overlap with TD-PD.