Highlights
Across Sweden and France, prevalence increased significantly from 2003 to 2022 for Parkinson disease (PD), multiple sclerosis (MS), and motor neuron diseases (MNDs), but the underlying drivers differed by disease.
For MS, rising prevalence appears to be driven largely by improved survival after diagnosis rather than a substantial increase in incidence.
For MNDs, the increase in prevalence was accompanied by rising crude and standardized incidence, supporting a genuine increase in disease occurrence.
For PD, prevalence rose modestly despite stable to declining incidence, suggesting that demographic aging and changes in post-diagnosis survival likely play larger roles than increasing disease onset.
Background and Clinical Context
Prevalence is one of the most visible epidemiologic signals in chronic neurologic disease, but it is also one of the easiest to misinterpret. A rising prevalence can reflect more people developing disease, better survival after diagnosis, population aging, broader ascertainment, or some combination of all four. For clinicians and planners, these distinctions matter. A survival-driven increase implies growing long-term care needs, whereas an incidence-driven increase points more directly toward changing environmental or behavioral risk exposures and the need for etiologic investigation.
PD, MS, and MNDs are all major neurologic causes of disability, yet they differ substantially in biology, age at onset, prognosis, and therapeutic landscape. MS has seen major advances in disease-modifying therapy and supportive care over the past two decades, making improved survival biologically and clinically plausible. PD has also benefited from improved multidisciplinary management, although disease-modifying therapy remains elusive and the condition is strongly influenced by population aging. MNDs, a group dominated in epidemiologic practice by amyotrophic lateral sclerosis and related disorders, remain associated with poor prognosis despite incremental gains in supportive care. Understanding whether more patients are living longer with these conditions or whether more patients are developing them in the first place has direct consequences for neurology services, rehabilitation capacity, respiratory support, palliative care, and public health research.
The present study by Guinebretiere and colleagues addresses this question using nationwide data from two European countries with robust administrative and health care systems: Sweden and France.
Study Design and Methods
Design and Population
This was a pair of nationwide, population-based retrospective cohort studies, analyzed together using pooled mixed-effects regression models with country treated as a random effect. The investigators included all individuals living in Sweden between 2001 and 2016 and all individuals living in France between 2009 and 2022. Temporal trend analyses focused on 2003 through 2022.
Diseases Studied
The analysis examined three major motor neurodegenerative disease groups: PD, MS, and MNDs. The main outcomes were temporal trends in prevalence, crude incidence, age-standardized and sex-standardized incidence, and age and life expectancy at diagnosis.
Why Standardization Matters
Crude incidence can appear stable even when underlying disease risk is changing, because it is heavily influenced by the age structure of the population. Standardized incidence adjusts for demographic shifts, allowing better inference about whether disease occurrence itself is changing over time. This distinction is particularly important for PD, whose occurrence rises sharply with age, and for cross-national analyses in populations with evolving age distributions.
Key Results
Prevalence Increased for All Three Diseases
In the pooled model, annual prevalence increased significantly for each disease over the study period. For PD, the prevalence ratio per year was 1.014 (p < 0.001), indicating a modest but consistent increase. For MS, the yearly prevalence ratio was 1.029 (p < 0.001), and for MNDs it was 1.028 (p < 0.001), both reflecting steeper rises than seen for PD.
These numbers may look small on a yearly basis, but compounded over nearly two decades they imply a substantial cumulative increase in the number of people living with each disease.
Parkinson Disease: Prevalence Rising Despite Stable-to-Declining Incidence
For PD, crude incidence remained nearly stable over time, with an incidence rate ratio per year of 0.998 (p < 0.001). Once standardized for age and sex, incidence declined more clearly, with an incidence rate ratio of 0.986 per year (p < 0.001). This divergence between crude and standardized estimates strongly suggests that demographic aging is masking a downward trend in the underlying rate of new diagnoses.
The life expectancy at diagnosis for PD showed a non-linear pattern. It increased from 2003 to 2013 by 0.95 months per calendar year (p < 0.001), then decreased from 2013 to 2022 by 1.20 months per calendar year (p = 0.002). This pattern complicates simple interpretation. Earlier gains in post-diagnosis survival may have contributed to the prevalence increase, while the later decline suggests either changing case mix, shifts in diagnostic timing, mortality pressures in later years, or other system-level effects. The central finding, however, is that rising PD prevalence does not appear to be explained by rising incidence.
Clinically, this aligns with the idea that the expanding PD population is being shaped more by aging populations and the long duration of illness than by an epidemic of new PD onset.
Multiple Sclerosis: A Predominantly Survival-Driven Increase
For MS, crude incidence was close to stable, with a slight decline over time (incidence rate ratio 0.992 per year, p < 0.001). Standardized incidence was even more stable, at 0.995 per year (p < 0.001), indicating little meaningful change in the underlying rate of new disease after demographic adjustment.
By contrast, life expectancy at diagnosis increased significantly across the entire study period, by 2.35 months per calendar year (p < 0.001). Among the three diseases studied, this is the clearest signal that rising prevalence is being driven by survival. Put simply, more patients with MS are living longer after diagnosis, and this is accumulating into a larger prevalent population.
This interpretation is biologically plausible and consistent with modern MS care. Over the last two decades, disease-modifying therapies have expanded substantially, earlier diagnosis has become more common, and multidisciplinary management of disability, bladder dysfunction, spasticity, infections, and comorbidity has improved. Importantly, improved survival does not necessarily mean absence of unmet need. A larger pool of long-surviving patients can increase demand for ambulatory neurology, imaging, rehabilitation, cognitive care, mental health support, pregnancy counseling, and progressive MS services.
Motor Neuron Diseases: Evidence for a True Increase in Incidence
MNDs showed the most concerning epidemiologic pattern. Both crude and standardized incidence increased over time: crude incidence rate ratio 1.018 per year (p < 0.001) and standardized incidence rate ratio 1.008 per year (p < 0.001). Because the increase persists after standardization, the data support a real increase in disease occurrence rather than a change explained solely by aging.
Life expectancy at diagnosis also rose modestly over the full study period, by 0.34 months per calendar year (p = 0.01). However, compared with the clear survival signal in MS, the magnitude here is small. The overall interpretation is that the rise in MND prevalence primarily reflects increasing incidence, with a lesser contribution from survival gains.
For clinicians and researchers, this finding is especially important. If more people are genuinely developing MNDs over time, the implication is not just increased care demand but also a potentially changing landscape of environmental, occupational, genetic, or gene-environment risk factors. The study does not identify causes, but it sharpens the question.
Clinical and Public Health Interpretation
The major contribution of this study is conceptual clarity. It shows that the same epidemiologic headline, rising prevalence, can mean very different things depending on the disease.
In MS, the rising prevalence appears to represent a partial success story of modern neurology. Better survival expands the number of patients living with disease, which should be interpreted as a marker of improved longitudinal care as much as disease burden. Health systems should therefore plan for chronic care capacity, not just acute diagnostic services.
In MNDs, by contrast, the data point more strongly toward an increase in disease occurrence. This raises priority questions for surveillance and etiologic research. Standardization reduces the possibility that the rise is merely demographic. While ascertainment changes can never be ruled out completely in observational studies, the consistency across two nations and the persistence after adjustment make a purely artifactual explanation less convincing.
For PD, the story is more mixed. The increase in prevalence is real but modest, and the incidence data argue against a true increase in onset rates. This reinforces the importance of distinguishing crude from standardized trends in age-sensitive disorders. Aging populations can sustain or raise crude counts even when the adjusted risk of diagnosis is falling.
Strengths and Limitations
Strengths
The study has several notable strengths. It used nationwide population-based data from two countries, reducing referral and center-level selection bias. The long observation window permits assessment of sustained trends rather than short-term fluctuation. The investigators also examined both crude and standardized incidence as well as life expectancy at diagnosis, which is essential for separating competing drivers of prevalence. Finally, pooling Sweden and France while allowing country-level random effects improves robustness without assuming the two systems are identical.
Limitations
As with any registry-based or administrative epidemiology study, disease ascertainment and coding accuracy are important limitations. Temporal changes in diagnosis, coding practices, neurologic service access, or registry completeness may influence measured incidence and prevalence. This concern is particularly relevant for MNDs, where heightened awareness and improved case capture could inflate temporal trends, although the cross-national consistency supports a more substantive signal.
Life expectancy at diagnosis is also not identical to disease-specific survival. It can be affected by lead-time phenomena, shifts in age at diagnosis, and competing mortality. The abstract does not provide detailed disease definitions, validation metrics, or subgroup analyses by age, sex, or phenotype, all of which will matter for deeper interpretation. In PD especially, the post-2013 decline in life expectancy at diagnosis deserves further exploration before any strong causal inferences are made.
Generalizability beyond Western Europe should be made cautiously. The findings are highly relevant to settings with similar demographics and health care access, but disease ascertainment, survival, and risk factor patterns may differ in lower-resource or genetically distinct populations.
Implications for Practice and Research
For health systems, the practical message is straightforward: prevalence growth does not translate into the same service needs across diseases. MS programs should prepare for larger long-term survivor populations with disability management and life-course care needs. MND services may need both more diagnostic capacity and expanded access to respiratory, nutritional, communication, and palliative support if incidence continues to rise. PD care planning should account for population aging and sustained demand for chronic neurologic and geriatric care even in the absence of increasing adjusted incidence.
For researchers, the study offers a roadmap for next steps. In MS, the obvious next questions concern which components of care are contributing most to improved survival and whether those gains are equitable across age, sex, geography, and socioeconomic groups. In MNDs, the incidence increase justifies renewed focus on environmental and occupational exposures, temporal birth-cohort effects, and cross-national harmonized surveillance. In PD, future work should clarify the interplay among aging, diagnostic behavior, subtype distribution, and survival trends.
Conclusion
This large binational analysis shows that rising prevalence in major motor neurologic diseases is not a single phenomenon. MS prevalence appears to be increasing mainly because patients are living longer after diagnosis. MND prevalence appears to be rising because more people are developing disease. PD prevalence is increasing modestly, largely independent of rising incidence and likely shaped by demographic aging and changing survival. These distinctions are clinically meaningful, epidemiologically instructive, and directly relevant to workforce planning, long-term care design, and disease-cause research.
Funding and Trial Registration
No ClinicalTrials.gov registration applies to this retrospective population-based observational study. Funding details were not provided in the abstract and should be confirmed from the full published article.
References
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