Substantia Nigra Neuromelanin Magnetic Resonance Imaging In Patients With Different Subtypes Of Parkinson Disease

Objective:Neuromelanin(NM)is a dark pigment that mainly exists in neurons of the substantia nigra pars compacta(SNc).In Parkinson disease(PD)patients,NM concentration decreases gradually with degeneration and necrosis of dopamine neurons,suggesting potential use as a PD biomarker.We aimed to evaluate associations between NM concentration in in-vivo SN and PD progression and different motor subtypes by using NM magnetic resonance imaging(NM-MRI).Methods:Fifty-four patients with idiopathic PD were enrolled.Patients were divided into groups by subtypes with different clinical symptoms: tremor dominant(TD)group and postural instability and gait difficulty(PIGD)group.Fifteen healthy age-matched volunteers were enrolled as controls.All subjects underwent clinical assessment and NM-MRI examination.Results:PD patients showed significantly decreased contrast-to-noise ratio(CNR)values in medial and lateral SN(P <0.05)compared to controls.CNR values in lateral SN region decreased linearly with PD progression(P = 0.001).PIGD patients showed significant decreases in CNR mean values in lateral SN compared to TD patients(P = 0.004).Diagnostic accuracy of using lateral substantia nigra(SN)in TD and PIGD groups was 79%(sensitivity 76.5%,specificity 78.6%).Interpretation:NM concentration in PD patients decreases gradually during disease progression and differs significantly between PD subtypes.NM may be a reliable biomarker for PD severity and subtype identification.