What Are MS Lesions?

Lesions, plaques, white spots or scars.  There are many names for the areas of destruction seen on an MRI of the central nervous system (CNS), all representing the same finding.  But what are these damaged areas and why do we see them as white spots on a MRI in a patient with Multiple Sclerosis (MS)?  

When a patient is suspected of having a disease such as MS, one of the first diagnostic tests performed is typically a MRI of the CNS.  The lesions noted on a MRI of the CNS represent the destruction of nerves illustrated on certain imaging sequences. There are demyelinating neurologic disorders affecting both the central or peripheral nervous system.  MS specifically involves the CNS, which is made up of the brain and spinal cord. It is the most common demyelinating disorder and commonest non traumatic cause of disability to affect young adults.  

The Role of Myelin in Lesions

When looking at the components of a nerve of the CNS, it is important to know the role of each anatomical part.  Many use the analogy of a wire you may see around your home, like a wire streaming from a lamp to the wall outlet.  The nerves of the CNS make up these “wires,” where the black protective coating is called myelin.  Myelin, or the myelin sheath, is a fatting tissue coating the nerve that protects the nerve from damage and efficiently conducts signals to other nerves and muscles.  In the lamp example, it is the black coating of the wire. When a myelin sheath is damaged, it results in loss of function to the nerve.   

For patients with MS, this damaged nerve struggles to send proper signals to the CNS and leads to symptoms.  Wherever the damage occurs will correspond with what symptoms manifest.  For example, if the myelin sheath of the optic nerve (the nerve that connects the eye to the brain) is damaged, it may result in painful eye movements and vision loss.   

Autoimmune Activity

One of the challenging components of MS is its highly variable presentation.  Although MS patients may have a constellation of similar symptoms throughout their course of the disease, there is no rhyme or reason for when these presentations will come about  in an individual’s journey.   What is known, regarding MS and the formation of MS lesions seen on a MRI of the CNS, is that it is felt to represent an autoimmune response.  It is not clearly known why this autoimmune response is triggered in patients with MS.  Genetic predisposition, environmental factors and perhaps even infectious causes have been connected to the autoimmune phenomena connected to MS, but to date there is no clear cause of the disease.   

The autoimmune activity within a MS patient unravels a cascade of factors which attack the myelin sheath and result in its damage.  On a cellular level, the destruction of the myelin sheath occurs as a result of macrophages and microglia, both pieces of a larger system of cellular components called to respond to the autoimmune system activation Similar can be seen in other disorders such as Neuromyelitis Optica Spectrum Disorder, Neurosarcoidosis, infections, vitamin deficiencies and toxin exposures.  This drives the importance of an accurate diagnosis of MS as a critical factor in patient care.  

Types of Lesions

The mainstay of how to visualize these white spots or lesions in cases of MS is on Magnetic resonance imaging (MRI).  Obtaining a MRI of the brain or spinal cord can assist with characterizing the location of these lesions.  MRI imaging is also helpful in classifying the timing of when a lesion has occurred. If you have ever experienced having a MRI image, you may relate to patients reporting these studies do take anywhere from 30 to 60 minutes for each part of the central nervous system imaged.  The need for this time during a MRI is related to multiple different image types needed.  

Patients often ask how long they have had a lesion or “how old” their lesions are. At times it can be a challenge to identify the timeline of when lesion had occurred.  Whenever possible, having older MRI imaging studies compared to resent studies is recommended.   Lesions can be classified in 3 general categories:   

• Acute or “active lesions” are identified by their uptake of Gadolinium dye used at times during MRI imaging.  This uptake in radiology terms is called “enhancement” and in most cases, lasts up to 12-15 weeks.  After that time, these active lesions no longer enhance.   

• T2 FLAIR lesions are the result of active lesions transitioning over to a more chronic appeareance lession. These lesions that are most typically referenced to in MS lesions. 

• Black hole lesions have damaged the nerve to such a degree that a resultant complete lack of function of that portion of the nerve has occurred, and are termed to reflect complete loss of the nerve tissue.  Unfortunately, the accumulation of these black holes have been linked to more pronounced disability as the tissue damaged can not be “fixed back” to any degree.  

In addition, MS lesions occurring in certain areas of the central nervous system have been linked to poorer outcomes. For instance, when MS attacks the brainstem and/or the spinal cord, research suggests that these patients tend to experience greater disability.  It is important to note that the location of MS lesions do impact a patient’s long term outcome.   

Treating MS Lesions

Fortunately, typical endpoints in most of the MS disease modifying treatments (DMTs) clinical trials include prevention of new MS lesions. Given that each MS DMT has a different mechanism of action, MS DMTs do vary in their ability to reach this goal. Looking to the future, MS research studies are investing in solutions for remyelinating or rebuilding the myelin of already damaged areas which is a foremost priority to diminish MS lesions and restore neurologic function. 

With more FDA-approved DMTs available, navigating your options can feel overwhelming, but Your Guide to MS Disease Modifying Therapies is designed to help you understand each treatment and what it can offer.