Beginner's Guide to MS: What is a Lesion?
Whether you have been diagnosed, in the process of being diagnosed, or wonder what it takes to get diagnosed with multiple sclerosis, it is likely that you have heard of LESIONS. Those scars (or plaques) which can be seen on MRI scans which show when the myelin has been damaged.
MYELIN is the fatty protein which creates an insulating sheath to protect nerve cells called AXONS. Myelin is part of the white matter in the brain and helps the electrical impulses of communication between the brain and parts of the body travel more quickly and efficiently. (see The Myelin Project for more information)
LESIONS occur where nerves have been demyelinated. So how does that happen?
The process of DEMYELINATION begins with inflammation. In the case of multiple sclerosis this happens in the CENTRAL NERVOUS SYSTEM (CNS) consisting of the brain and the spinal cord.
Think for a moment of a time when you accidentally cut a finger and decided against washing the wound immediately. The invaders of germs and bacteria are detected by the IMMUNE SYSTEM which sends in a team of specialized white blood cells, called LEUKOCYTES, to fight and destroy the invaders. Perhaps the wound became red and inflamed while the battle was underway.
In multiple sclerosis, a breach in the Blood-Brain-Barrier allows specialized white blood cells, called T-CELLS, to travel from the blood stream into the CNS. Once these ‘killer’ T Cells mistake myelin for foreign invaders and go on the attack, they produce CYTOKINES which destroy myelin and which also recruit MACROPHAGES to help destroy myelin and cut the nerve fibers.
Also, B-CELLS can travel into the CNS and become specialized white blood cells, called PLASMA, which then release antibodies to destroy myelin. It can truly be a gruesome scene in there with confused white blood cells destroying the very white matter in the CNS which is necessary for our electrical system to function effectively. (see the MS Center of Excellence for a cartoon depicting the demyelination process)
At the same time, regulatory T-CELLS enter the battle and release protective cytokines which “turn off” the destructive white blood cells. Then OLIGODENDROCYTES are furiously trying to lay down new myelin before being destroyed themselves. INFLAMMATION and DEMYELINATION are the result of this battle and can be seen upon MRI imaging. Depending upon the sequence of imaging (ie. T1-weighted, T2-weighted, FLAIR, etc), the resulting LESIONS may appear darker, lighter, or even white on film.
With the use of a contrast agent, called GADOLINIUM which is injected into the blood stream, breaches in the Blood-Brain-Barrier and active lesions can be seen very clearly. Active lesions are the ones which we MS patients often say look like “lights on a Christmas tree.” They show that the disease is highly active at that time and are called ENHANCED LESIONS on the MRI report.
A different type of lesion is often called a BLACK HOLE which is believed to be evidence of AXONAL LOSS, meaning that the nerve fibers are “dead.” Not all active lesions turn into black holes due to the busy work of the oligodendrocytes. Go REMYELINATION!!!
Ultimately, what is the significance of lesions?
Do more lesions equate to more disability? No.
Do fewer lesions equate to less disability? No.
Do the placement of lesions correlate to specific symptoms? Yes, No, and Maybe.
Can the appearance of lesions change from week to week? Yes.
So. Why do we care so much about lesions?
Detecting lesions on an MRI scan helps to gather enough evidence for a diagnosis of MS. Monitoring disease activity helps to determine if a patient’s choice of DISEASE-MODIFYING TREATMENT is working sufficiently. A large change in lesion load can guide the neurologist in deciding on a change in treatment plan, if necessary.
And, admit it - Lesions are fun to look for when you’ve just had an MRI and are looking at the pretty pictures of your insides on the CD of the images you brought home.
You did ask for a copy of the MRI images on CD didn't you?