Multiple sclerosis (MS) is an inflammatory disease that affects the central nervous system (CNS), including the brain and spinal cord. MS relapses, symptoms, and disability progression can be very different from person to person. Some people with MS may have slow disease progression and few relapses, whereas others progress faster and experience more attacks. The reasons for these differences aren’t well understood.

One recent discovery by researchers involves specific brain lesions called “smoldering MS lesions.” Smoldering lesions may indicate subtle disease processes linked to faster progression.

What Is Smoldering Multiple Sclerosis?

Smoldering MS is an ongoing process that keeps making your MS worse, even when you’re feeling good. The presence of slowly expanding lesions — also called smoldering lesions, rimmed lesions, and chronic active lesions — is associated with smoldering MS. These brain lesions remain active for a long time and can continue to grow over many years, damaging the nerves in the brain areas where they’re located.

“Smoldering MS is not necessarily new, but it’s come to the forefront of discussion,” according to Dr. Aaron Boster, a medical doctor and founder of the Boster Center for Multiple Sclerosis. He explained that people with MS can get worse in two ways — from MS attacks or relapses and from “progression independent of relapse activity … where you’re not having an attack, but you are getting worse.” The second process is that of smoldering MS.

Smoldering Lesions vs. Other MS Lesions

Smoldering lesions have dark boundaries that are visible by magnetic resonance imaging (MRI) when using a special technique called susceptibility weighted imaging. This viewing technique is sensitive to the presence of certain compounds, such as iron.

The lesions’ dark rims (also called “paramagnetic rims”) are partly due to the presence of iron-rich microglia on the lesion border. Microglia are immune cells of the central nervous system. The dark rims are a sign that the immune system is attacking nerves in that area. This continued attack can cause further nerve damage and neuroinflammation (inflammation within the CNS), resulting in worsening of MS.

MS brain lesions that don’t have a dark rim are common. Called “non-rim lesions,” they may get smaller and even go away over time.

Rimmed lesions remain stable or may even grow due to ongoing demyelination (damage to the protective myelin sheath that covers nerve fibers). Demyelination and nerve damage disrupt the messages being sent from the brain and spinal cord to other parts of the body.

Ongoing neuroinflammation caused by smoldering lesions may be especially damaging to the brain. More demyelination may occur, affecting surrounding tissue and preventing remyelination (repair of the myelin sheath). The presence of more smoldering lesions has been associated with more aggressive MS and more neuron cell death.

What Causes Smoldering Multiple Sclerosis?

Smoldering MS is like a hidden enemy that keeps making your MS worse, even when you’re in remission (a period of reduced or no symptoms) and no new brain lesions have been detected. Scientists think it’s a big reason people with MS get more disabled over time.

The recent discovery of slowly expanding lesions has contributed to this idea. These lesions are like tiny fires that keep burning, even if you can’t see them. Researchers have noted that it can be difficult to detect smoldering MS in clinical practice because doctors don’t routinely use susceptibility weighted imaging.

How Is Smoldering Multiple Sclerosis Detected?

Scientists are working on new imaging methods that may help detect smoldering lesions in the neurology clinic. Researchers have also noted that other tools may help detect smoldering MS and disability progression in the future.

Scientists are also trying to find better ways to measure disease activity and track how MS is progressing. This research is important because it could eventually help doctors diagnose and treat smoldering MS earlier.

What Are the Symptoms of Smoldering Multiple Sclerosis?

Currently, no symptoms are specifically associated with smoldering MS. The condition causes ongoing worsening of disability with MS, even when you’re feeling all right and have no new brain lesions. This gradual worsening, which can continue in times of remission, is called progression independent of relapse activity. It’s different from worsening during a relapse.

Rimmed lesions have been found in people with progressive MS and in people with relapsing-remitting MS. Researchers have noted that people who have more rimmed lesions tend to have worse problems with movement and thinking at a younger age, even if they’re on MS treatment.

Both relapses and smoldering MS may contribute to disability progression for people with MS. Disability worsening caused by smoldering MS can be very subtle and hard to notice in the doctor’s office. That’s why researchers are looking for new clinical tools to help detect these small changes over time. These tools might include smart devices to help track your health and MS progression more closely.

Are Treatments Available for Smoldering Multiple Sclerosis?

The various types of MS treatments include disease-modifying therapies (DMTs), which can help reduce the number of relapses and the amount of brain damage. Other therapies help manage MS symptoms or treat attacks associated with a relapse.

Current DMTs don’t work directly on smoldering MS lesions. According to Dr. Boster, some of them “can impact smoldering MS, but they are not in and of themselves addressing that aspect of disease.”

These DMTs can’t cross the blood-brain barrier, which is like a protective wall around your brain. Scientists have identified smoldering lesions in people with MS taking DMTs and noted the need for new therapies that can target smoldering MS.

Treatments on the Horizon

One promising option is a new class of medications called Bruton’s tyrosine kinase (BTK) inhibitors, which are tiny molecules that can cross the blood-brain barrier. BTK inhibitors work by interrupting signals between certain immune cells (B cells) that are involved in MS. BTK inhibitors are being tested in clinical trials to see if they can slow or stop the damage caused by smoldering MS.

Lifestyle Factors

Scientists have found that some lifestyle factors can affect brain health and make smoldering MS worse. These factors include:

• Not exercising
• Eating poorly
• Smoking
• Drinking too much alcohol
• Not sleeping well
• Taking certain medications
• Having other health problems

It’s important to consider all these factors when making a treatment plan for your MS. Taking care of your overall health can help you manage your MS better.

Talk With Your Doctor

If you have questions regarding smoldering MS or your specific MS symptoms, it’s important to contact your neurologist or another health care provider. A health care provider can answer your questions, recommend any changes to your MS treatment plan, and help you understand how to live your best with MS. Ensuring regular follow-up medical visits is key to maintaining your overall health with MS.

Talk With Others Who Understand

MyMSTeam is the social network for those living with multiple sclerosis and their loved ones. On MyMSTeam, more than 213,000 members with MS come together to ask questions, offer support and advice from their experience, and share their stories with others who understand life with MS.

Have you discussed smoldering MS with your health care provider or noticed a subtle progression of your MS? Share your experience or start a conversation by posting on your Activities page.