Daniel M. Keller, PhD

July 20, 2015

SAN DIEGO — Clinicians have long relied on self-reports by patients with movement disorders to monitor disease activity and medication effectiveness, but now wearable activity monitors may give a clearer picture of overall mobility. In a study of patients with Parkinson's disease (PD), researchers found that the monitors gave a truer picture of patients' ventures out into the community.

The study involved 54 community-dwelling patients with early to midstage PD. They wore wireless inertial measurement units incorporating small accelerometers with GPS (global positioning system) sensors (WIMuGPS) during waking hours for 14 days. They were also asked to report in a diary any movement they made outside of their own property.

"For numerous individuals, even though that they reported they have high life space outside, or high mobility outside, they may actually have not gone outside very much at all, as well as of course those individuals that have gone outside," Lynn Zhu, MSc, a PhD student in epidemiology and biostatistics at Western University in London, Ontario, Canada, reported here at the 19th International Congress of Parkinson's Disease and Movement Disorders (MDS).

There was good validity between the WIMuGPS and self-assessments using the diary on the outcomes of duration of time outside as well as the frequency of trips outside the home.

"However, we're not able to establish good validity between the WIMuGPS and self-report measure on life space size," she said. Life space is important because it allows one to understand how far and wide people are traveling outside, which is an indicator of their real-life performance, she noted.

Patients had a mean age of 67.8 years, and two thirds were men. They were diagnosed with PD 6.4 years earlier and had Hoehn and Yahr stage 1-3 disease. They had no orthopedic, musculoskeletal, or other neurologic conditions and did not use mobility assistive devices.

There was good convergent validity between the diary results and the WIMuGPS records. However, correlation was not as good for the Life Space Assessment (life space size, an indication of mobility outside the home).

Table. Correlation of Diary and WIMuGPS Records

Assessment Correlation (r Value) P Value
Daily time sampled outside (%) 0.693 <.001
Hourly no. of trips outside 0.427 .0013
Life space assessment (size) 0.393 .0033


Given the GPS tracking of movement within the community, it is a reasonable assumption that the WIMuGPS gave a more accurate assessment of life space than did the diary.

"Most individuals on most days recorded on the WIMuGPS more trips outside as well as more time outside than they self-reported," Ms Zhu said. "So that lets me conclude that Life Space Assessment as well as possibly other types of cross-sectional reports of one's own mobility may not be able to distinguish what's actually happening between individuals with different types of mobility or different quantities of mobility.

"We were able to demonstrate for the first time that a GPS and wearable sensors like the WIMuGPS are reliable and valid alternatives for self-report measures," she concluded.

Although the diaries and the sensors correlated well for frequency and duration outside, when it comes to assessing the actual quantity of the life space, "the WIMuGPS may be a better approximation than the existing way of just asking people cross-sectionally 'What was your mobility like?' since the last time you've seen them," she advised clinicians.

The WIMuGPS may be a better approximation than the existing way of just asking people cross-sectionally 'what was your mobility like?' Lynn Zhu

The investigators noted that the general population has over-reported time outside in their diaries in contrast to patients with PD, who under-reported the duration. Clinicians and researchers will need meaningful standards against which to compare duration and frequency of trips outside.

Zhu cautioned that each kind of sensor is designed and calibrated differently and so must be validated as a good alternative to self-reports before it can be used it in clinical applications.

Ken Kubota, BS (computer science and electrical engineering), director of data science at the Michael J. Fox Foundation for Parkinson's Research, commented to Medscape Medical News that miniaturization of accelerometers and electronics is opening new possibilities for the use of wearable sensors.

"This is pretty exciting stuff," he said. "It'll be objective; it'll be an accurate way for physicians to take a look at the data and make clinical decisions from that data."

The advantage of sensors over patient reports is that people can have poor recall, memory and reporting may be tainted by perception (eg, whether to call a stumble a fall or not), and people are often not consistent in filling out diaries.

"If something is more troublesome, we tend to kind of log it as a longer duration than it actually has been or actually a shorter duration if it's not all that troubling," he noted. Furthermore, sleep duration is notoriously hard to log, and even more so, the quality of sleep.

"It's what makes prescribing medication for Parkinson's disease more of a dark art than a science," Kubota said. Beyond knowing PD patients' "on" and "off" times and being an aid to medication prescribing, wearable sensors are helping to monitor and quantify PD symptoms to correlate them with their biological origins, more finely identify subtypes of the disease, and identify targets for drug development," he explained.

Sensors can monitor mobility, dyskinesia, and bradykinesia but can also measure sleep patterns and autonomic variables. such as heart rate, blood pressure, body temperature, and sweating, as well as incorporate medication reminders.

There was no commercial funding for the study. Ms Zhu has disclosed no relevant financial relationships. Mr Kubota is an employee of the Michael J. Fox Foundation for Parkinson's Research.

19th International Congress of Parkinson's Disease and Movement Disorders (MDS). Abstract 1219. Presented June 15, 2015.


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