Prediction of the Unified Parkinson’s Disease Rating Scale assessment using a genetic programming system with geometric semantic genetic operators
Introduction
Neurological disorders, including Parkinson’s disease (PD), affect profoundly the lives of patients and their families (Caap-Ahlgren & Dehlin, 2002). PD is a disorder of the central nervous system that leads to severe difficulties with body motions. It is the second most common neurodegenerative disorder after Alzheimer’s disease (de Rijk et al., 2000) and it is estimated that more than one million people in North America alone are affected by it (Lang & Lozano, 1998). Moreover, as explained in Little, McSharry, Hunter, Spielman, and Ramig (2009), because of the rapid increase in the average population age in several countries, and since the risk of contracting PD increases after the age of 60 (Van Den Eeden et al., 2013), this number is expected to rise in the next few years. As a direct consequence, the medical care costs for patients with PD is estimated to rise in the future (Huse et al., 2005). The currently available therapies aim at improving the functional capacity of the patient for as much time as possible; however they are not able to modify the progression of the neurodegenerative process (Singh, Pillay, & Choonara, 2007). Most people affected by PD will therefore be substantially dependent on clinical intervention.
The process of tracking PD symptoms progression is a complex task. It often uses a system of measurement of the intensity of the symptoms called Unified Parkinson’s Disease Rating Scale (UPDRS). The UPDRS is a scale that was developed as an effort to incorporate elements from existing scales to provide a comprehensive, efficient and flexible way of measuring and monitoring PD-related disability and impairment (Movement Disorder Society, 2003). Prior to its development, multiple scales were used in different hospital clinics and health centers, making comparative assessments difficult. One of the core advantages of the UPDRS is that it was developed as a compound scale to capture multiple aspects of PD. It assesses both motor disability and motor impairment. Of all analogous available clinical scales, the UPDRS is currently the most commonly used one (Ramaker, Marinus, Stiggelbout, & Van Hilten, 2002). It reflects the presence and severity of symptoms, expressing it in a range from 0 to 176, with 0 representing a healthy state and 176 total disability. The UPDRS contains three sections:
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Mentation, Behavior and Mood.
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Activities of daily living.
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Motor.
The motor section of the UPDRS encompasses tasks such as speech, facial expression, tremor and rigidity and expresses the severity of the related symptoms in a range from 0 to 108, where 0 represents a symptom free state and 108 denotes severe motor impairment.
For many persons affected by PD, the necessary specialized medical examinations to estimate the severity of their symptoms are difficult and invasive and they have to be performed by trained medical staff. Thus, as described in Tsanas, Little, McSharry, and Ramig (2010), symptom monitoring is costly and logistically inconvenient for patients and clinicians. All these critical aspects highlight the need of reliable and accurate computational techniques that allow estimating the UPDRS automatically and effectively.
In this paper, we present a comparative study of a set of computational methods aimed at predicting the severity of the PD symptoms in their entirety (i.e. including all of the three sections of the UPDRS) and the severity of the symptoms considered in the motor section of the UPDRS. The studied methods attempt to express these quantities as a function of several other features related to patients. Thus, the application is reduced to two symbolic regression problems, using as many datasets. The two datasets contain identical features and differ between each other in terms of the target values to be predicted. The dataset using as target the values of the severity of the general PD symptoms (including all of the three sections of the UPDRS) will be called total-UPDRS from now on, while the one using as target the values of the severity of the motor symptoms will be called motor-UPDRS.
In particular, the focus of this paper is on an intelligent system based on genetic programming (Koza, 1992, Poli et al., 2008). We use a recently introduced version of genetic programming, that uses so called geometric semantic genetic operators. We compare the results obtained with this new version of genetic programming to the ones returned by standard genetic programming and a set of different state-of-the-art machine learning methods.
The paper is organized as follows: Section 2 introduces standard genetic programming. Section 3 presents and motivates geometric semantic genetic operators. Section 4 describes the data we used and our experimental settings and proposes an accurate analysis of the results, comparing them with several different machine learning techniques. Finally, Section 5 concludes the paper.
Section snippets
Genetic programming
Models lie in the core of any technology in any industry, be it finance, health, manufacturing, services, mining, or information technology. The task of data-driven modeling lies in using a limited number of observations of system variables for inferring relationships among these variables. The design of reliable learning machines for data-driven modeling tasks is of strategic importance, as there are many systems that cannot be accurately modeled by classical mathematical or statistical
Geometric semantic operators
In the last few years, GP has been extensively used both in Industry and Academia (Arcuri and Yao, 2010, Chan et al., 2010, Choi and Choi, 2012, dos Santos et al., 2011, Koza et al., 2008, Moreno-Torres et al., 2013, Ravisankar et al., 2010, Trujillo et al., 2012, Yeun et al., 2000, Wongseree et al., 2007) and it has produced a wide set of results that have been defined human-competitive (Koza, 2010). While these results have demonstrated the appropriateness of GP in tackling real-life
Data set
This study makes use of the recordings described in Goetz et al. (2009) and in Tsanas et al. (2010), where 52 subjects with idiopathic PD were recruited. A subject was diagnosed with PD if he had at least two of the following: rest tremor, bradykinesia (slow movement) or rigidity, without evidence of other forms of parkinsonism. The study was supervised by six US medical centers: Georgia Institute of Technology (7 subjects), National Institutes of Health (10 subjects), Oregon Health and Science
Conclusions
The process of tracking Parkinson’s disease (PD) symptoms progression is very complex and new and powerful computational methods are needed to automatize it and make it faster and more reliable. The objective of this paper was to present a computational intelligence method that could outperform the state-of-the-art ones in terms of prediction accuracy of the PD symptoms progression, automatically discovering insightful relationships between dysphonia measures and the well known Unified
Acknowledgments
This work was supported by national funds through FCT under contract PEst-OE/EEI/LA0021/2013 and by projects MassGP (PTDC/EEI-CTP/2975/2012), EnviGP (PTDC/EIA-CCO/103363/2008) and InteleGen (PTDC/DTP-FTO/1747/2012), Portugal.
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