Multiple sclerosis MRI technique can spot tissue damage months before an MS attack
July 15, 2013
A study published in this week’s Neurology found that a relatively new MRI technique could spot changes in the brain up to three months before inflammation causes a multiple sclerosis (MS) attack.
Traditionally, we have viewed MS as a disease where the immune system attacks the brain, causing the abrupt onset of inflammation (measured by gadolinium enhancement). This inflammation causes damage to the brain, which causes symptoms.
The new technique, called susceptibility-weighted imaging, allows researchers to see that tissue damage is happening up to three months prior to the inflammation.
Susceptibility-weighted imaging measures the amount of magnetic susceptibility of tissues aligned in different directions. The amount of alignment in different directions is called the phase image. In tissues like myelin, the magnetic susceptibility lines up with the direction of the myelin because molecules can move alongside the myelin more easily than they can move across it.
When myelin is damaged, the tissue becomes disorganized and magnetic susceptibility changes from aligning primarily in one direction to alignment in many different directions. The phase image can be used to measure the degree of myelin damage.
In this study, 20 patients underwent monthly MRI scans for six months. During this time, researchers found 43 newly active MS lesions found in nine of the patients. They found the lesions by injecting gadolinium, a dye used in MRI imaging which measures the breakdown of the blood-brain barrier that happens when MS lesions form.
Using the technique, researchers were able to take newly active MS lesions and look back in time for changes in the MRI at that location. The phase images at the site of these newly inflamed MS lesions showed changes up to three months prior to the inflammation. Areas of the brain that were not involved in the inflammation did not show these changes.
Recent studies using other MRI techniques have similar findings. For example, magnetization transfer measures the integrity of large molecules in myelin, and shows changes happening up to 6 months prior to enhancement. Studies like this have caused researchers to revise their theories about what might cause damage in MS lesions.
It appears that damage may be happening months before the onset of inflammation. However, we still do not know the full meaning of this. Is there a low level of smoldering inflammation that suddenly “takes off” after a few months? Is there some other process that damages the myelin first like a virus, toxin or other process, that then leads to activation of the immune system once a certain amount of tissue damage has occurred? Studies like this one will make important contributions in identifying the cause of MS.