Abstract
Parkinson's disease is now considered a complex, multi-peptide, central, and peripheral nervous system disorder with considerable clinical heterogeneity. Non-motor symptoms play a key role in the trajectory of Parkinson's disease, from prodromal premotor to end stages. To understand the clinical heterogeneity of Parkinson's disease, this study used cluster analysis to search for subtypes from a large, multi-center, international, and well-characterized cohort of Parkinson's disease patients across all motor stages, using a combination of cardinal motor features (bradykinesia, rigidity, tremor, axial signs) and, for the first time, specific validated rater-based non-motor symptom scales. Two independent international cohort studies were used: (a) the validation study of the Non-Motor Symptoms Scale (n = 411) and (b) baseline data from the global Non-Motor International Longitudinal Study (n = 540). k-means cluster analyses were performed on the non-motor and motor domains (domains clustering) and the 30 individual non-motor symptoms alone (symptoms clustering), and hierarchical agglomerative clustering was performed to group symptoms together. Four clusters are identified from the domains clustering supporting previous studies: mild, non-motor dominant, motor-dominant, and severe. In addition, six new smaller clusters are identified from the symptoms clustering, each characterized by clinically-relevant non-motor symptoms. The clusters identified in this study present statistical confirmation of the increasingly important role of non-motor symptoms (NMS) in Parkinson's disease heterogeneity and take steps toward subtype-specific treatment packages.
Highlights
Parkinson’s disease (PD) is classically considered a motor disorder, with resting tremor, rigidity, bradykinesia, and postural instability and gait disorder as its core features
The significant clinical heterogeneity of non-motor symptoms (NMS) in PD suggests the existence of specific non-motor subtypes (Marras and Chaudhuri, 2016; Sauerbier et al, 2016)
It has been argued that the recent concept of non-motor endophenotypes of PD provides a stronger basis for subtyping, since these relate to the central pathophysiology of specific neurotransmitter systems and are likely to remain stable over time (Marras and Chaudhuri, 2016)
Summary
Parkinson’s disease (PD) is classically considered a motor disorder, with resting tremor, rigidity, bradykinesia, and postural instability and gait disorder as its core features. The concept of PD has changed considerably in the last few years, prompting a revision of its diagnostic criteria to include non-motor symptoms (NMS) in the core parameters (Postuma et al, 2015; Marras and Chaudhuri, 2016). The significant clinical heterogeneity of NMS in PD suggests the existence of specific non-motor subtypes (Marras and Chaudhuri, 2016; Sauerbier et al, 2016). It has been argued that the recent concept of non-motor endophenotypes of PD provides a stronger basis for subtyping, since these relate to the central pathophysiology of specific neurotransmitter systems and are likely to remain stable over time (Marras and Chaudhuri, 2016). No studies have used cluster analysis techniques to examine subtypes present in NMS only
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