New diagnostic guidelines for multiple sclerosis could help doctors identify the disease earlier, including in people without typical symptoms, but researchers say the changes will fundamentally reshape how MS clinical trials are designed and conducted. The 2024 updates to the McDonald criteria, the internationally recognized framework for diagnosing MS, aim to catch the disease sooner when treatment may be most effective. However, experts caution that these changes carry risks of overdiagnosis and require urgent development of better tools to predict which patients will actually benefit from treatment.

What Changed in the New MS Diagnostic Criteria?

MS is a chronic autoimmune disorder in which the immune system mistakenly attacks myelin, the protective coating around nerve fibers in the brain and spinal cord. When myelin is damaged, communication between the brain and body breaks down, leading to symptoms like numbness, vision problems, mobility impairment, and cognitive difficulties.

The McDonald criteria, first published in 2001, have been revised several times as scientific understanding of MS has advanced. The most recent revision, developed in 2024 and formally published in 2025, includes several key changes intended to support earlier and more accurate diagnosis. These changes include:

• Diagnosis without dissemination in time: Earlier versions required evidence that MS-related damage occurred at different points in time. Under the new criteria, MS may be diagnosed without that evidence in certain circumstances, as long as clinical and test findings point to MS and other possible causes have been ruled out.
• Asymptomatic and atypical presentations: The 2024 criteria allow MS to be diagnosed in some people without typical symptoms when MRI scans and other tests meet specific requirements and other possible causes have been excluded.
• Unified disease framework: Historically, MS was divided into relapsing MS, which involves flares followed by recovery, and progressive MS, in which disability gradually worsens. The new criteria propose a single framework recognizing that MS is a disease spectrum with overlapping characteristics rather than distinct categories.

The rationale behind these changes reflects growing scientific evidence that MS begins biologically well before typical clinical symptoms appear. By identifying and treating people with subclinical disease early, researchers hope to prevent clinical disability from developing in the first place.

Why Are Experts Concerned About Overdiagnosis?

While earlier diagnosis sounds beneficial, the expanded criteria carry real risks. Misdiagnosis, meaning an incorrect diagnosis, and overdiagnosis, meaning diagnosing a disease that would not have caused harm if left untreated, are significant concerns. Many MS therapies are costly and carry safety risks, making it crucial to identify which patients truly need treatment.

Researchers emphasize that better biomarkers are urgently needed to predict future MS activity and help identify which patients are most likely to benefit from treatment. Without these tools, clinicians may struggle to distinguish between people who genuinely need early intervention and those who might never develop disabling disease.

How Will Clinical Trials Need to Change?

One of the most significant implications of the updated criteria is that clinical trials testing new MS therapies will require major redesign. Historically, trials were designed differently for relapsing and progressive MS. Now that the diagnostic framework recognizes MS as a spectrum rather than distinct categories, trial design must evolve accordingly.

Additionally, disease activity and severity in modern trials are generally lower than in older trials, likely because earlier diagnosis under evolving criteria means people receive treatment sooner. This lower baseline disease activity makes it harder for researchers to detect meaningful differences between treatment and placebo groups, potentially requiring new outcome measures and study designs.

Researchers noted that a major overhaul of clinical trial design will require input from all relevant stakeholders, including people living with MS, clinicians, scientists, industry, and regulators. Concerted efforts in this direction are urgently needed to identify treatments that can repair, protect, and definitively alter the biological mechanisms underlying progressive disease.

What New MS Treatments Are in Development?

While diagnostic criteria are evolving, researchers are also pursuing novel therapeutic approaches that target the underlying cause of MS rather than just managing symptoms. One emerging strategy focuses on protecting and restoring myelin itself, the nerve coating that MS damages.

Quantum BioPharma is developing Lucid-MS, a drug candidate that takes a fundamentally different approach from existing MS therapies. Rather than modulating the immune system, Lucid-MS targets protein arginine deiminase 2 (PAD2), an enzyme directly involved in myelin degradation. The goal is to protect and potentially restore the myelin sheath itself, addressing the underlying cause of disability rather than managing symptoms.

In preclinical animal models, Lucid-MS accelerated functional recovery, preserved myelin, and reduced damage in MS mouse models. Phase 1 clinical trials in healthy human volunteers confirmed a favorable safety profile, with the drug well tolerated and no significant safety concerns reported. In March 2026, the company submitted an Investigational New Drug application to the U.S. FDA for a phase 2 trial.

Supporting the phase 2 development is an ongoing imaging collaboration with Massachusetts General Hospital. The study uses a novel PET imaging tracer called [18F]3F4AP, developed by researchers at MGH and Harvard Medical School. The tracer is designed to directly visualize demyelinated neurons with intact axons, offering a more precise way to measure myelin damage and repair than any currently available technique. Enrollment in the pilot study recently reached its halfway point, with early imaging data showing a robust signal in acute MS lesions.

Steps to Understanding Your MS Diagnosis Options

• Ask about diagnostic criteria: If you have been recently diagnosed with MS or are undergoing diagnostic testing, ask your neurologist whether they are using the updated 2024 McDonald criteria and how this may affect your diagnosis and treatment plan.
• Discuss biomarker testing: Talk with your healthcare provider about whether biomarker tests are available to help predict your disease course and determine which treatments are most likely to benefit you specifically.
• Explore clinical trial opportunities: If you are interested in accessing newer treatment approaches like myelin-protective therapies, ask your neurologist about clinical trials in your area or whether you might be eligible for studies testing novel approaches.

The global MS therapeutics market was valued at approximately $27.4 billion in 2024 and is projected to reach $38.6 billion by 2030, reflecting the large and persistent unmet clinical need in MS treatment. As diagnostic criteria evolve and new therapeutic approaches emerge, the landscape of MS care is shifting toward earlier intervention and more targeted treatment strategies.