Wrist-worn activity trackers may predict MS progression before standard tests can

American Academy of Neurology / Johns Hopkins University

The standard tests for measuring disability in multiple sclerosis were not designed to catch small changes. A neurologist can assess walking speed, check reflexes, test cognitive function during a clinic visit. But these snapshots, taken every few months, can miss the slow, subtle shifts that signal a disease turning worse. By the time a standard exam picks up progression, months of decline may have already passed unnoticed.

A study published in Neurology suggests that a simple wrist-worn device, the kind of accelerometer found in commercial fitness trackers, might detect those shifts earlier. Researchers at Johns Hopkins University tracked 238 people with MS for an average of three years and found that changes in daily activity patterns predicted both worsening disability and loss of brain volume.

Activity patterns that signal trouble

Participants wore the devices 24 hours a day for two-week stretches, repeating the measurement every three months. The sensors recorded how much light, moderate, and vigorous physical activity each person had, how much time they spent sitting, and their circadian rhythms.

During the study, 120 of the 238 participants experienced disease progression. The strongest predictor was a decline in daytime activity levels. People whose activity dropped in the first half of the day were about 20% more likely to have worsening disability compared with those whose patterns stayed stable.

Morning activity, specifically between 8:00 a.m. and 10:00 a.m., proved particularly telling. Every standard deviation decline in morning activity was associated with a 0.18% decrease in whole brain volume, a 0.34% decrease in deep gray matter volume, and a 0.35% loss in the thalamus, a brain region involved in relaying sensory and motor signals.

Correlation, not causation

The researchers are careful to note what the study does not show. It does not prove that declining activity causes MS to progress. The relationship could run the other direction: early, subclinical disease worsening might make people less active before they or their doctors notice anything wrong. The wearable data may be detecting a consequence of progression rather than a contributor to it.

That distinction matters for patients, who might otherwise conclude that exercising more would slow their disease. The study provides no evidence for that claim. What it does suggest is that activity data could serve as an early warning system, flagging patients who need closer monitoring or a change in treatment before conventional assessments would raise the alarm.

Limitations worth noting

The study population was relatively older, with an average age of 55, and had been living with MS for an average of 13 years. Their average disability score of 3 on the Expanded Disability Status Scale placed them in moderate territory: able to walk without assistance but experiencing noticeable impairment. Whether the same activity-based signals would appear in younger patients with milder disease remains unknown.

The study also lacked a control group of people without MS. That means the researchers could not determine how much of the observed activity decline was normal aging versus disease-specific. Separating those two signals will be important for any future clinical application.

Participants had no other serious health conditions that could affect their physical activity and had not experienced an MS relapse within six months before enrolling. Those exclusion criteria helped isolate the MS signal but also mean the findings may not apply to patients with more complex medical profiles.

A cheap tool with an expensive potential

The appeal of wearable sensors is practical. They are inexpensive, widely available, and require nothing from the patient beyond wearing them. Compared with brain MRI scans, which cost hundreds of dollars and require specialized equipment, a wrist-worn accelerometer is almost trivially easy to deploy.

If future studies confirm these findings, wearable data could be integrated into routine MS care as a continuous monitoring tool between clinic visits. It could also accelerate clinical trials by providing a sensitive, objective measure of disease activity that does not depend on infrequent neurological exams.

The gap between that potential and clinical reality is still significant. But the data suggest the signal is there, waiting in the patterns of how people move through their mornings.