Locus Coeruleus Shows a Spatial Pattern of Structural Disintegration in Parkinson's Disease

BACKGROUND: Parkinson's disease (PD) causes a loss of neuromelanin‐positive, noradrenergic neurons in the locus coeruleus (LC), which has been implicated in nonmotor dysfunction. OBJECTIVES: We used “neuromelanin sensitive” magnetic resonance imaging (MRI) to localize structural disintegration in the LC and its association with nonmotor dysfunction in PD. METHODS: A total of 42 patients with PD and 24 age‐matched healthy volunteers underwent magnetization transfer weighted (MTw) MRI of the LC. The contrast‐to‐noise ratio of the MTw signal (CNR(MTw)) was used as an index of structural LC integrity. We performed slicewise and voxelwise analyses to map spatial patterns of structural disintegration, complemented by principal component analysis (PCA). We also tested for correlations between regional CNR(MTw) and severity of nonmotor symptoms. RESULTS: Mean CNR(MTw) of the right LC was reduced in patients relative to controls. Voxelwise and slicewise analyses showed that the attenuation of CNR(MTw) was confined to the right mid‐caudal LC and linked regional CNR(MTw) to nonmotor symptoms. CNR(MTw) attenuation in the left mid‐caudal LC was associated with the orthostatic drop in systolic blood pressure, whereas CNR(MTw) attenuation in the caudal most portion of right LC correlated with apathy ratings. PCA identified a bilateral component that was more weakly expressed in patients. This component was characterized by a gradient in CNR(MTw) along the rostro‐caudal and dorso‐ventral axes of the nucleus. The individual expression score of this component reflected the overall severity of nonmotor symptoms. CONCLUSION: A spatially heterogeneous disintegration of LC in PD may determine the individual expression of specific nonmotor symptoms such as orthostatic dysregulation or apathy. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson Movement Disorder Society.