When Octave Guinebretière first started crunching the numbers from two of the world's most comprehensive health databases, he expected to find a clear signal of emerging crisis. Instead, the epidemiologist from Pitié-Salpêtrière Hospital uncovered something more nuanced — and ultimately more encouraging than headlines about "rising brain disease" suggest. Across France and Sweden, hundreds of thousands of patient records spanning nearly two decades reveal that the steady increase in neurodegenerative disease prevalence conceals very different stories: some populations growing sicker, others simply living longer. The findings, published in the journal Neurology, offer a more hopeful picture than the raw numbers imply.
Guinebretière, alongside Thomas Nedelec from the ARAMIS research team at the Paris Brain Institute, drew on the French National Health Data System — which covers 99% of France's population — and Sweden's national health registers, in continuous operation since the 1960s. Their study tracked patients from 2001 to 2016 in Sweden and 2009 to 2022 in France. "Both countries have high-performing, centralized health care systems with universal coverage," Guinebretière explains. "These administrative health databases allow us to describe population health in a satisfactory way, drawing on data from reimbursable care."
The most striking finding concerns multiple sclerosis. While MS prevalence rose by 2.9% per year between 2003 and 2022 — a figure that might sound alarming — deeper analysis reveals a different reality. The number of new diagnoses remained roughly stable over the period. What changed was how long patients lived after diagnosis: an average of 2.35 additional months with each passing year. "We are diagnosing roughly as many MS cases today as 20 years ago," Nedelec notes. "But patients are living significantly longer thanks to better clinical management and therapies that can alter the trajectory of the disease." The expanded arsenal of immunosuppressive and immunomodulatory treatments has fundamentally altered what an MS diagnosis means.
For amyotrophic lateral sclerosis, the picture is more complex. ALS incidence is genuinely rising — by 1.8% annually — but population aging accounts for 56% of that increase, since the disease typically develops around age 70. Improved awareness has also led to better detection. Environmental or lifestyle factors may play a smaller role, with regional clustering of cases still not fully understood.
Parkinson's disease showed the most modest increase in prevalence, at 1.4% per year, though the researchers identified a surprise element in their data that complicates the straightforward narrative.
What unites these findings is a call for more granular public health thinking. "A rise in prevalence can be driven by patients living longer, by more people falling ill, or simply by population aging," Guinebretière says. Untangling those threads matters enormously for policy: MS's rising prevalence signals success in extending life, demanding investment in long-term care quality, while ALS's true increase warrants different investigative and preventive approaches. Understanding which trend drives the numbers makes all the difference for the patients behind them.