Benefits of objectively measuring Parkinson’s disease motor symptoms

Parkinson’s disease (PD) is a complex neurological disorder characterized by progressive motor symptoms that affect a patient’s mobility, balance and quality of life. The gold standard for evaluating PD symptoms has primarily relied on subjective assessments during in-clinic visits using rating scales like the Unified Parkinson’s Disease Rating Scale (UPDRS). This approach, however, has specific limitations, leading to often incomplete disease progression evaluation.

First-generation approach – in-person clinical evaluation

The most common method today to determine the existence and progression of PD is through in-person clinical evaluation. These are typically 20- to 30-minute clinic appointments that occur relatively infrequently. During the appointment, the clinician questions the patients about their symptoms and overall well-being while observing the patient and carrying out a physical examination. Based on this information, the clinician may determine the symptom rating.

Clinical rating scales are used to quantify the symptoms, impairment and disability [1]. The Unified Parkinson’s Disease Rating Scale (UPDRS) has been one of the principal tools used to evaluate PD motor symptoms and is still used widely today. Using this method, clinicians assess various motor symptoms based on observations, patient-reported experiences and their expertise.

An in-person clinical evaluation using rating scales, when appropriate and within the allocated appointment time, is the current gold standard in evaluating PD severity and tracking the progression of the disease. However, according to clinicopathological studies in the UK and Canada, diagnostic accuracy of the method is low. [6]

The UPDRS was originally developed in the 1980s to evaluate various aspects of PD, including motor and non-motor experiences in daily living and motor complications. The Movement Disorder Society recently made changes to the UPDRS to take a more holistic approach, adding non-motor elements, such as mood and behavior. [3]

Another commonly used rating scale is Hoehn and Yahr, originally created in 1967 to evaluate the disease severity by combining deficiency and disability based on bilateral motor involvement and compromised balance and gait. The simple scale describes PD stages from 1 to 5 based on motor impairment severity and disability. The scale has gained acceptance due to its ease of use, although it does not fully reflect a person’s degree of impairment when it comes to handling daily living activities. [1]

Shortcomings of in-person clinical evaluation

In-person clinical evaluations during time-restricted appointments, however, have inherent limitations. The assessment performed in a clinical environment does not mirror day-to-day symptoms, which may vary during the day or even between days. In-clinic evaluations only capture a “snapshot” of the symptoms at a specific moment in time. In addition, the evaluations are highly subjective. [4]

Subjectivity

The evaluation is highly dependent on subjectivity across human examiners, as it relies heavily on the clinician’s own expertise, skills and experience. The in-clinic evaluation is subject to interpretability issues and recall bias, including a risk of assessment disagreement among the professionals working on the same patient case [1]. In addition, many elements depend greatly on the patient’s memory and the ability to describe the symptoms experienced, either during the appointment or with the help of a symptom diary. Also, information entered in diaries is often unclear. A study by Erb et al. [2] found that 38% of all participants who were to complete a motor symptom diary at home missed about 25% of the possible entries, while the average delay time was more than 4 hours. To create an optimized and personalized PD treatment plan, objective evaluation of the patients’ symptoms and overall condition is crucial.

Time limitations

Clinic visits generally tend to happen infrequently, restricting comprehensive patient monitoring and timely intervention. Clinic visits are also often restricted by short consultation times, limiting the length of evaluation to the duration of the appointment. Some signs of disease progression may remain unnoticed during the examination. Furthermore, this overlooks typical motor symptom fluctuations that patients may experience at home and between appointments.

Non-home environment

The clinic environment and potential travel to the clinic can also impact the patient’s condition and the evaluation of symptoms during the appointment. In many cases, patients also strive to perform at their best during medical evaluation, known as the Hawthorne effect in which patients modify their behavior in response to their awareness of being observed. Therefore, assessment in a non-home environment can easily lead to decisions that do not accurately represent the daily symptoms the patient experiences at home.

Long-term follow-up challenges

Lack of continuous, objective monitoring hinders a more complete understanding of the treatment effectiveness over extended periods. The optimal management of PD motor symptoms and their complications depends primarily on consistent symptom detection in frequent intervals, leading to enhanced treatment decisions.

Decisions, often made based on short-term evaluations and subjective information, can detrimentally affect the treatment plan by not considering a comprehensive, longer-term view of symptom occurrence and evolution over time.

Second-generation approach – adding motion measurement

Over the last decades, methods using motion measurement have been developed to overcome the shortcomings of the first-generation approach. They provide a non-invasive method to measure the movements of PD patients, even in a home environment.

Methods using motion measurement are not intended to replace the first-generation approach but to complement it. The approach can help clinicians get more insight into a patient’s condition at home.

Motion measurement uses dedicated wearable devices with motion sensors or accelerometer data from a smartwatch to quantify physical movements when assessing a patient’s symptoms.

Over the past years, an increasing number of new wearable solutions have been launched to measure and monitor movement disorder symptoms, showing promising results in research trials. These wearable devices can be used either during a clinic visit or remotely. [1]

Studies show that remote and continuous monitoring plays a crucial role in the treatment quality a patient receives by allowing medical professionals to better track disease progression and adjust medication. Additionally, remote and continuous monitoring with wearable devices plays a significant role in reducing healthcare system costs and raising patient satisfaction. [1]

Advantages of symptom monitoring with wearable motion sensors

Recently, wearable devices have started to be used in clinical practice for monitoring a patient’s PD-related motor symptoms during daily activity. Statistical analysis has shown potential in symptom detection, and the correlation between the severity and the expert evaluations has been high.