The 2024 McDonald Criteria Explained by an MS Specialist: What Patients Need to Know About the New MS Diagnosis Guidelines

Doctors have updated the guidelines for diagnosing multiple sclerosis (MS) in 2024, known as the "McDonald Criteria". New changes now include the optic nerve as a fifth key location, expanded spinal fluid tests, and more detailed MRI features that can confirm MS earlier and more safely. These updates can help you get diagnosed more accurately and start treatment sooner, while also reducing the risk of misdiagnosis.

If you have MS or think you might, here's a clear, patient-friendly summary of what these 2024 changes mean for you.

Are You Worried You Might Have MS?

If you're reading this because of concerning symptoms, an abnormal MRI, or uncertainty about your diagnosis, you're not alone. Getting these test results can be frightening, and waiting for answers is often one of the most stressful parts of the process. Here's what you should know:

• Not everyone with white matter lesions on MRI has MS – many other conditions can cause similar findings, including migraine, small vessel disease, and normal age-related changes
• Meeting some criteria doesn't mean you have MS – doctors must carefully rule out other conditions that mimic MS first
• The McDonald criteria are complex – they require specialist interpretation and cannot be self-applied
• Early evaluation matters – if you're concerned, seeing an MS specialist is the best next step

This guide will help you understand what your neurologist is looking for, so you know what to ask for when you see an MS specialist. Only a qualified specialist can diagnose MS using these criteria.

Why Does the 2024 Update of the McDonald Criteria Matter?

The new guidelines help doctors:

• Diagnose MS earlier, sometimes at your first visit if the evidence is strong enough
• Use more precise tests (like advanced MRI patterns and updated spinal fluid markers)
• Apply the same rulebook to relapsing MS, progressive MS, and most children and adults
• Avoid misdiagnosis, especially in older patients or those with migraine or blood vessel (vascular) disease

Early and accurate diagnosis means earlier treatment, which can slow MS progression and improve your quality of life.

Understanding Your Risk: What Increases or Decreases the Likelihood of MS

It's natural to wonder where you fall on the diagnostic spectrum. While only an MS specialist can weigh all factors together, understanding what makes MS more or less likely can help frame your questions and concerns.

Signs that INCREASE the likelihood your findings are MS:

• You're between ages 20-50 (the most common age range for MS onset)
• You've had typical MS symptoms like optic neuritis (vision changes with eye pain), isolated numbness or weakness, or balance problems
• Your MRI shows lesions in multiple typical MS locations, especially both brain and spinal cord
• You have positive spinal fluid tests (oligoclonal bands or elevated kappa free light chain index)
• Your lesions show the "central vein sign" or other MS-specific patterns on advanced MRI

Signs that DECREASE the likelihood your findings are MS:

• You're over age 50 with no prior neurological symptoms
• You have vascular risk factors (high blood pressure, diabetes, smoking, high cholesterol)
• You have a history of migraines or headaches
• Your MRI lesions are only in one location or don't fit typical MS patterns
• Your symptoms are better explained by another condition

Remember: This is not a checklist you can use to diagnose yourself. MS diagnosis requires careful clinical judgment, ruling out other conditions, and proper application of the McDonald criteria by an MS specialist.

Key Changes and Why They Matter

1. MRI Scans Are Now Central to Diagnosis

The 2024 criteria make it clear that paraclinical tests, especially MRI, are essential in almost all cases of suspected MS.

Your neurologist will now nearly always use:

• Brain MRI
• Spinal cord MRI
• Sometimes optic nerve MRI

to look for typical MS lesions and to help rule out other conditions.

Why it matters:

• MRI is now the backbone of MS diagnosis, not just a “nice-to-have.”
• Purely “clinical” diagnoses (without imaging) are now not recommended.
• This helps avoid misdiagnosis and ensures your treatment is based on clear, objective evidence.

2. The Optic Nerve Now Officially Counts Toward Diagnosis

The 2024 criteria now treat the optic nerve as a fifth key location in the central nervous system (CNS). Doctors look for typical MS lesions in five regions:

1. Periventricular (around the brain’s fluid-filled spaces)
2. Cortical / juxtacortical (near the brain’s surface)
3. Infratentorial (brainstem or cerebellum)
4. Spinal cord
5. Optic nerve

Optic nerve involvement can be picked up by:

• MRI scans of the optic nerve
• OCT scans (a quick, painless eye imaging test)
• Visual evoked potentials (VEPs, which measure how fast your brain responds to visual signals)

Why it matters:

• If you’ve had optic neuritis (blurry vision, eye pain with movement, washed-out colors), that episode can now officially count as one of the “MS spots” your doctor needs for diagnosis.
• This change can speed up diagnosis, especially in people who start with vision problems.

3. Easier, Faster Spinal Fluid Test: Kappa Free Light Chains

Spinal fluid (from a lumbar puncture/spinal tap) remains an important part of MS diagnosis in many cases.

Traditionally, doctors looked for oligoclonal bands (OCBs) in spinal fluid. The 2024 criteria now say that another marker, the kappa free light chain (kFLC) index, can be used instead and is considered equivalent to OCBs.

Why it matters:

• The kFLC index is:

  • Easier to run in many hospital labs
  • Faster and more objective than traditional OCB testing
  • Just as good at showing immune activity inside the brain and spinal cord

• For you, this means more accessible and reliable testing and fewer delays while waiting for specialized lab results.

4. New MRI Signs to Identify MS: Central Vein Sign & Paramagnetic Rim Lesions

The 2024 criteria formally recognize two “advanced” MRI features that can strengthen an MS diagnosis in tricky situations:

• Central Vein Sign (CVS)
  Many MS lesions form around small veins. On special MRI sequences, if a tiny vein runs through the middle of a white matter lesion, it supports an MS diagnosis.

• Paramagnetic Rim Lesions (PRLs)
  Some chronic MS lesions have a dark rim on certain MRI scans, suggesting ongoing smoldering inflammation that is very typical for MS.

These features are not required for diagnosis, but can be used:

• When MRI lesions could be from migraine, aging, or small vessel disease
• When only one main area of the CNS shows lesions and doctors need added specificity
• In some radiologically isolated syndrome (RIS) or non-typical presentations

Why it matters:

• CVS and PRLs give your neurologist extra tools to tell MS apart from look-alike conditions.
• Using them can reduce misdiagnosis and prevent unnecessary MS treatments in people who don’t truly have MS.

5. Diagnosing MS Even When You Haven’t Had Typical Symptoms (RIS)

Sometimes MRIs (done for headaches or trauma, for example) reveal white matter lesions that look very much like MS, even though you’ve never had a clear MS attack. This is called Radiologically Isolated Syndrome (RIS).

Under the 2024 criteria, MS can be diagnosed in high-risk RIS-like situations when:

• There are MS-typical lesions in at least two of the main locations (brain/spinal cord/optic nerve), and
• There is also clear evidence of ongoing MS-like disease activity, such as:
  • Lesions that clearly change over time (new spots or enhancing lesions), or
  • Positive spinal fluid (OCBs or kFLC index), or
  • A strongly MS-like pattern of lesions with the central vein sign

Why it matters:

• You might be offered treatment earlier, even before your first typical attack, if your overall risk of developing MS is high.
• This could help delay or prevent symptoms, though your neurologist will carefully balance benefits and risks.

6. Stricter Checks for Older Adults and People with Vascular Risk Factors

As we age, white matter spots on MRI become more common for reasons other than MS, such as:

• High blood pressure
• Diabetes
• High cholesterol
• Smoking
• Migraine
• Small vessel (vascular) disease

These can mimic MS on MRI. The 2024 criteria specifically warn that people aged 50 and older, or those with vascular risk factors, have a higher risk of misdiagnosis if doctors rely on brain lesions alone.

For these patients, doctors are now strongly encouraged to look for at least one of the following in addition to brain lesions:

• Spinal cord lesions typical of MS
• Positive spinal fluid (OCBs or kFLC index)
• An MS-like pattern with the central vein sign on MRI

Why it matters:

• If you’re older or have vascular risk factors, your neurologist will be extra cautious before labeling your MRI as “MS.”
• This reduces the risk of being treated for MS when the real problem is vascular, migraine-related, or something else.

7. Less Waiting for “Proof Over Time”

Traditionally, doctors often waited to see if more lesions or relapses appeared over time before confirming MS. The 2024 criteria recognize that, in many people, the risk of waiting outweighs the benefit.

Now, if you already have:

• Typical lesions in at least two of the five key locations, and
• Positive spinal fluid (OCBs or kFLC index), and
• No better explanation for your symptoms and MRI findings,

your doctor may be able to diagnose MS without waiting for a second attack or new lesions.

Why it matters:

• You may get a confirmed diagnosis and start treatment sooner, instead of waiting for your MS to “declare itself” with more damage.
• You still benefit from careful follow-up, but you don’t have to suffer a second attack just to “prove” the diagnosis.

8. One Unified Framework: Relapsing, Progressive, and Pediatric MS

The 2024 criteria also simplify who the rules apply to:

• Relapsing and Progressive MS now use one unified diagnostic framework. Progressive MS (gradual worsening over at least 12 months) still must show that slow progression, but the same MRI and spinal fluid rules are used, with special attention to spinal cord lesions in progressive cases.
• Children and teenagers are now diagnosed using the same basic criteria as adults, with extra care to rule out conditions like MOG-antibody disease. In younger children, additional blood tests are strongly recommended to avoid mislabeling them with MS.

Why it matters:

• Whether your MS started with clear relapses, slow progression, or in childhood, your neurologist is now using the same updated rulebook, with age- and situation-specific safeguards.

How Doctors Use the 2024 McDonald Criteria in Practice

In everyday clinic visits, here’s how neurologists generally apply the 2024 McDonald Criteria to diagnose MS:

1. Understand Your Symptoms and Exam Findings
   Your doctor reviews your history (such as vision changes, numbness, weakness, balance problems, bladder issues, or neurological symptoms like muscle twitching) and performs a detailed neurological exam to see which parts of the brain, spinal cord, or optic nerves might be involved.

2. Look for Lesions in the Right Places (Dissemination in Space)
   MRI of the brain and spinal cord – and sometimes the optic nerve – is used to check for typical MS lesions in at least two of these five areas:

   • Periventricular (around the brain’s fluid-filled spaces)
   • Cortical / juxtacortical (near the brain’s surface)
   • Infratentorial (brainstem or cerebellum)
   • Spinal cord
   • Optic nerve

3. Check for Evidence of Ongoing MS-like Activity
   Doctors look for signs that your immune system is actively affecting the central nervous system, using:

   • MRI, to see if some lesions are new or “active” (enhancing with contrast), and/or
   • Spinal fluid tests, to look for oligoclonal bands or an elevated kappa free light chain (kFLC) index

   In more complex cases, advanced MRI markers like the central vein sign or paramagnetic rim lesions can further support that the pattern truly looks like MS.

4. Rule Out Other Conditions
   Blood tests, imaging, and sometimes additional spinal fluid tests are used to exclude other causes that can look like MS, such as:

   • Infections
   • Vitamin deficiencies
   • Neuromyelitis optica spectrum disorder (NMOSD)
   • MOG-antibody associated disease (MOGAD)
   • Vascular (blood vessel) disease or severe migraines

5. Apply the Criteria to Your Situation
   Depending on your pattern, doctors may:

   • Diagnose relapsing MS if you’ve had attacks and your MRI/spinal fluid fit the 2024 rules
   • Diagnose progressive MS if you’ve had gradual worsening over about 12 months plus supporting MRI or spinal fluid findings
   • Diagnose MS in high-risk RIS (radiologically isolated syndrome) when your MRI and spinal fluid strongly suggest MS, even if you haven’t had a classic clinical attack yet

6. Discuss Treatment and Monitoring
   Once the criteria are met and other causes are ruled out, your neurologist will talk with you about:

   • Starting a disease-modifying therapy (DMT)
   • The frequency of follow-up MRIs
   • How to monitor for relapses or progression over time

The goal of the 2024 McDonald Criteria is simple: make it easier to diagnose true MS early and safely, while avoiding misdiagnosis.

What Do These Changes Mean for You?

It's normal to feel anxious while reading medical information like this. Here's what the 2024 updates mean in practical terms:

• Earlier Diagnosis and Treatment
  Strong MRI and spinal fluid evidence may now be enough to diagnose MS without waiting for more relapses or new lesions—so you might start treatment sooner and potentially prevent future damage.

• More Accurate Diagnoses
  New tools (optic nerve involvement, CVS, PRLs, kFLC index) help your neurologist separate true MS from other causes of white matter lesions, giving you more confidence in your diagnosis.

• Better Protection Against Misdiagnosis
  If you're older or have vascular risk factors, doctors are encouraged to get extra evidence before calling it MS. This reduces the chance of starting powerful MS medications when you don't actually have MS.

• More Inclusive Criteria
  People with RIS, progressive symptoms from the start, or pediatric-onset MS are all now covered in a single, coherent framework, making the diagnosis process clearer and up-to-date across ages and disease types.

Next Steps If You're Concerned About MS

• See an MS Specialist
  A neurologist specializing in MS can apply the 2024 McDonald Criteria correctly and help you understand where you stand. Consider scheduling a specialized multiple sclerosis evaluation to get a comprehensive assessment using the latest diagnostic guidelines.

• Review Previous MRIs
  Older scans may now meet the updated criteria even if you were told "not enough for MS" before. Always bring your actual MRI images—not just the reports.

• Ask About Spinal Fluid Tests (Including kFLC)
  If a spinal tap is recommended, ask whether your center can test kappa free light chains as well as oligoclonal bands.

• Consider Eye Exams
  If you've had vision problems, ask about optic neuritis, OCT, and VEPs. These can now officially contribute to your MS diagnosis.

• Stay Informed and Ask Questions
  The criteria may sound technical, but your neurologist should be able to explain how your own MRI, spinal fluid, and symptoms fit into the 2024 framework. Don't hesitate to ask.

What If Your Diagnosis Is Still Uncertain?

Many people don't get a clear "yes" or "no" answer right away, and it's normal to feel frustrated when you're in diagnostic limbo. You might hear terms like:

• "Possible MS" or "suspected MS" – Your MRI or symptoms are suggestive, but don't yet meet full criteria for a definitive diagnosis
• "CIS" (Clinically Isolated Syndrome) – You've had one MS-like attack, but there isn't yet enough evidence for a full MS diagnosis
• "RIS" (Radiologically Isolated Syndrome) – Your MRI shows MS-like lesions, but you haven't had clear symptoms yet

If you're in diagnostic limbo:

• This is common – MS can be genuinely difficult to diagnose definitively at first, especially early in the disease course
• You're not being dismissed – Your neurologist is being appropriately cautious to avoid misdiagnosis and unnecessary treatment
• You may still benefit from monitoring – Regular MRIs can track whether lesions change over time, helping clarify the diagnosis
• Some people never develop MS – Not everyone with CIS or RIS progresses to full MS
• Ask about the watch-and-wait plan – Know exactly when you'll have follow-up scans and what specific changes would prompt treatment or a diagnosis

Your neurologist should explain clearly where you fall on the diagnostic spectrum and what the monitoring plan is if things change.

Final Thoughts

The 2024 McDonald Criteria represent a major step forward in diagnosing MS—earlier when it truly is MS, and more cautiously when it might not be.

If you’ve been told your MRI is “suspicious but not definite,” or if your diagnosis was made years ago without the benefit of these updated tools, it may be worth a fresh review with an MS specialist.

If you have questions about MS, want a second opinion, or would like an updated review of your case under the 2024 criteria, contact Dr. Achillefs Ntranos MD, our top-rated MS specialist in Los Angeles and Beverly Hills. Early, accurate and effective action can make a significant difference.

Frequently Asked Questions About the 2024 McDonald Criteria and MS Diagnosis

What are the 2024 McDonald criteria for MS?

The McDonald criteria are guidelines neurologists use to diagnose MS. The 2024 update refines how MRI lesions, spinal fluid findings, and clinical attacks are combined to confirm or rule out MS more accurately.

What changed in the 2024 McDonald criteria compared with earlier versions?

The 2024 update places more emphasis on certain MRI patterns and spinal fluid markers and clarifies how quickly a diagnosis can be made in high-risk situations. The article explains these changes in patient-friendly language.

How do MRI findings count toward the McDonald criteria?

MRI scans show whether lesions are in typical MS locations and whether there is evidence of lesions occurring at different times. Together, these features help demonstrate "dissemination in space and time," which is central to MS diagnosis.

What role do spinal fluid tests like oligoclonal bands or kappa free light chains play?

Abnormal spinal fluid immune markers can support an MS diagnosis, especially if MRI findings are borderline. They also help distinguish MS from some mimicking conditions.

Can I be diagnosed with MS if I don't meet the McDonald criteria yet?

If you don't fully meet the criteria, you may be labeled as having a clinically isolated syndrome or at risk of MS. In that case, your neurologist usually recommends careful monitoring and sometimes early treatment depending on your risk profile.

Should I get a second opinion about my MS diagnosis?

Because MS is a lifelong diagnosis, it is reasonable to seek a second opinion—especially if your symptoms, MRI, or spinal fluid results don't clearly fit. An MS specialist can review your case in the context of the latest criteria.

Can I have MS if my MRI is normal?

It's rare but possible, especially early in the disease. Spinal cord MRI and optic nerve imaging may show lesions even when brain MRI appears normal. Some people also have MS primarily affecting the spinal cord.

How many lesions do I need to have MS?

There's no specific number that defines MS. What matters is whether lesions appear in at least two of the five key locations (periventricular, cortical/juxtacortical, infratentorial, spinal cord, optic nerve) and show the typical MS pattern.

My doctor mentioned "waiting to see if more lesions appear." Why wait?

The 2024 criteria allow earlier diagnosis in many cases, but if findings are borderline or other conditions haven't been fully ruled out, watching for changes over time can prevent misdiagnosis and avoid starting you on powerful medications unnecessarily.

Can the McDonald criteria be wrong?

No diagnostic criteria are perfect. That's why neurologists must also carefully rule out other conditions (called "differential diagnosis") before confirming MS. The 2024 criteria include specific safeguards to reduce misdiagnosis.

I was diagnosed with MS before 2024. Do I need to be re-evaluated?

If your diagnosis was clear and you're doing well on treatment, probably not. But if there was uncertainty about your diagnosis, or if you were told you "almost" met criteria before, a review under the 2024 guidelines might be worthwhile.

What if I disagree with my neurologist's conclusion?

It's completely reasonable to seek a second opinion from an MS specialist, especially for something as significant as an MS diagnosis. Bring all your MRI images (not just reports), test results, and a detailed symptom history to the appointment.

About the Author

Dr. Achillefs Ntranos MD

Board-Certified Neurologist
Achilles Neurology Clinic

Dr. Achillefs Ntranos MD is a board-certified neurologist and MS specialist known for his thorough evaluations and compassionate approach. Originally from Greece, he trained at Johns Hopkins University and Mount Sinai Hospital before founding Achilles Neurology Clinic in Beverly Hills to deliver comprehensive, patient-centered neurological care. He specializes in MS, autoimmune neurology, neuropathy, headaches, and other neurological disorders, blending research-driven insights with personalized treatment plans.

Learn More About Dr. Ntranos(310) 774-7025

The information in this guide is for educational purposes and should not replace individualized medical advice. Always consult with your healthcare provider about your specific situation.

References:

1. Diagnosis of multiple sclerosis: 2024 revisions of the McDonald criteria