Parkinson’s disease (PD), multiple sclerosis (MS), and motor neuron disease (MND) appear to be increasingly prevalent, but for different reasons, according to analyses of Swedish and French registry data reported in Neurology. “These findings indicate that the rising MS prevalence is largely survival-driven and the rising MND prevalence reflects a true increase in incidence, whereas PD prevalence grows modestly, largely independent of incidence,” corresponding author Thomas Nedelec, PhD, of Sorbonne University in Paris, and coauthors wrote.

Multiple Drivers of Rising Prevalence

In pooled analyses of the Swedish (2003-2016) and French (2011-2022) health registers, the researchers found that prevalence rose annually by 1.4% for PD, 2.9% for MS, and 2.8% for MND (all P<0.001). Age at diagnosis stayed relatively stable in both countries and for all three diseases, making earlier detection an unlikely explanation for the trends, except for MS in Sweden in the early 2000s, which coincided with expanded access to MRI.

Although crude incidence held nearly steady for PD and MS, and even dipped slightly for PD after age standardization, both crude and standardized MND incidence rose consistently in the pooled analysis. This suggests that factors beyond demographic aging, such as environmental exposure or healthcare access, may drive the rising MND incidence.

Longer life expectancy at MS diagnosis largely explains the disease’s growing prevalence. By contrast, the deceleration of life expectancy gains in PD between 2013 and 2022 compared with gains in the prior decade may account for the recent stabilization in PD prevalence. Life expectancy for patients with MND showed no clear gain, suggesting its rising prevalence is due to a true increase in incidence.

“Depending on the mechanism that drives prevalence, whether increased incidence reflecting changing risk factor exposures, improved survival due to therapeutic advances, or demographic aging of the population, inferences about underlying causes differ substantially between PD, MS, and MNDs, with direct implications for health care planning and etiologic research,” Dr. Nedelec and colleagues wrote.

An Outside Expert’s Comments on the Study

 Physician’s Weekly spoke with Ted Dawson, MD, PhD, a professor of neurology at the Johns Hopkins University School of Medicine, about the study and its implications for patient care.

Physician’s Weekly: Why was it important to conduct this study?

Dr. Dawson: It was important to disentangle whether the rising burden of major motor neurodegenerative diseases reflects more people developing these conditions, patients living longer with them, or both. Without that distinction, clinicians and health systems may misinterpret increasing case numbers as purely an incidence phenomenon and misdirect resources to prevention versus long‑term care.

In Sweden and France, life expectancy at PD diagnosis improved over time, then plateaued or declined since 2010. How should this affect how physicians counsel newly diagnosed patients about their future?

These data suggest that, at a population level, gains in survival after PD diagnosis have slowed or even reversed in the past decade while life expectancy in the general population continued to rise. For newly diagnosed patients, this argues for a realistic but balanced message: PD remains a chronic, often slowly progressive disorder, but we should avoid overpromising continuous survival improvements based on older projections.

The authors conclude that rising MS prevalence is due to patients living longer, not to more new cases appearing. What does that suggest about the role of disease-modifying therapies and the need for improved access to these therapies?

The finding that MS prevalence is increasing mainly because patients are living longer, while incidence is stable or slightly declining, strongly points to the impact of disease‑modifying therapies and improved overall care. It suggests that modern MS management is successfully extending life expectancy and likely delaying disability accrual, rather than simply uncovering more cases.

Unlike PD and MS, both crude and standardized MND incidence increased over the study period. What, beyond population aging, might be driving this increase?

Because MND incidence is rising, even after age  and sex standardization, the signal cannot be explained solely by population aging. Possible contributors include changing environmental or occupational exposures, better recognition and referral pathways, and increased survival from competing causes, which allow more individuals to reach ages at which MND risk peaks.

These data come from Sweden and France, two high-income countries with universal healthcare. What should clinicians in other health systems keep in mind before applying these trends to their own patient populations?

These trends from two high‑income countries with universal coverage and robust registries may not directly generalize to settings with different access to neurologists, imaging, and disease‑modifying drugs. Clinicians elsewhere should consider local diagnostic practices, environmental exposures, and availability of therapies before extrapolating absolute rates or survival estimates to their own patients.

What other comments would you like to share with clinicians?

One practical lesson is that “more patients in clinic” does not always mean more new cases. In MS, it often reflects successful long‑term management that keeps people alive and under follow‑up. Clinicians should anticipate larger cohorts needing chronic care, particularly for MS, and integrate neurorehabilitation, mental health, and social support into routine practice.