When Maria started losing her vision, she didn't know that silent changes had been happening inside her brain for years. Multiple sclerosis had been quietly damaging her nervous system long before she felt anything wrong. By the time doctors finally put a name to her illness, the disease had already done permanent damage.
That story could soon become less common, thanks to a major shift in how doctors diagnose multiple sclerosis. In 2024, the international guidelines doctors use to identify the disease — called the McDonald criteria — received their most significant overhaul in a decade. The changes now make it possible to detect MS before symptoms even appear.
Dr. Jiwon Oh, director of the BARLO MS Centre at St. Michael's Hospital in Toronto, was among the experts who helped rewrite these guidelines. Now she and nearly 30 of the world's leading MS clinicians have published a commentary in the journal Nature Medicine, breaking down what the changes mean and what comes next.
"The 2024 revisions were the biggest change ever made to the most fundamental criteria in our field, all aimed at improving outcomes for people with MS," Oh said.
For decades, diagnosing MS meant waiting. Patients had to experience multiple flare-ups — waves of symptoms like numbness, vision problems, or weakness — before doctors could confirm the disease. That meant years of uncertainty while damage accumulated silently.
The 2024 changes flip that approach. Doctors can now check the optic nerve — the pathway connecting the eye to the brain — as a key place to spot MS. Newer spinal fluid tests, more widely available than before, offer another confirmation tool. Advanced MRI scans can distinguish MS from other conditions that historically looked similar, reducing the chance of confusing it with something else.
The shift reflects a deeper change in how scientists understand the disease. Rather than treating MS as separate subtypes, research increasingly shows it as one spectrum where both relapses and progression happen together in most people. The new criteria reflect that thinking with a single framework for diagnosis, regardless of a patient's age or how the disease shows up.
Oh and her colleagues caution that catching MS earlier isn't without risks. Loosening criteria can sometimes mean misdiagnosing people who don't have MS. The commentary outlines safeguards: requiring MRI confirmation whenever possible, using very specific new imaging tools, and adding extra checks for children and older adults where mistakes are more likely.
Access remains uneven. Some newer diagnostic tools need specialized equipment and expertise not available in every hospital or country. The commentary calls for better ways to predict how each person's disease will progress and for faster clinical trials so new treatments reach patients sooner.
But for people like Maria, the direction is clear. The goal isn't just to name the disease earlier — it's to give people more time to act before it takes its toll.