Researchers from The Netherlands report that they were able to distinguish between people with MS who had cognitive impairment (such as memory and concentration problems) and those who did not, based on brain scans using a specific type of imaging (DTI, or diffusion tensor imaging). The study suggests that loss of nerve-insulating myelin, more than the loss of nerve cells, may be a key factor in cognitive problems, and supports the approach of using DTI as one way to measure the impact of potential therapies aimed at protecting the nervous system from MS damage. The study, by Hanneke Hulst, MSc, Frederik Barkhof, PhD, and colleagues at the VU University Medical Center (Amsterdam) was recently published
in the journal Neurology in March 2013.
This study was funded by the Dutch MS Research Foundation.
Background: Cognitive impairment
is a common problem in MS, but how it is related to damage to certain parts of the brain is not completely understood.
Improvements in imaging technology are important tools for improving our ability to have fast readouts on the success of MS treatments under study. Conventional magnetic resonance imaging (MRI) detects tissue disruption, but is a limited measure of the degree of tissue injury and its recovery. Diffusion tensor imaging provides a measure of tissue injury that may differentiate damage to the myelin coating that insulates nerve fibers (axons) from damage to the axon itself.
The study compared 35 people with MS without cognition problems, 20 people with MS with cognition problems, and 30 healthy people without MS. Participants were categorized as cognitively impaired or cognitively normal according to the results of tests that examined verbal memory and learning, information processing speed, and spatial, working, and long-term memory. People with MS were considered cognitively impaired if they scored poorly on a minimum of two of these five tests.
All participants underwent MRI scanning and MR diffusion tensor imaging to measure the integrity and detect areas of damage in various parts of the brain. The images were analyzed to look for differences in white matter (containing nerve fibers whose myelin is attacked and destroyed in MS), gray matter (containing the nerve cells that perform brain functions), and particular brain structures.
They found that in people with MS who had normal cognition, DTI detected abnormalities in 49% of the white matter regions they investigated, compared to 76% of such regions in people with cognitive problems. In other words, people with impaired cognition had 50% more white matter damage than people with MS without impaired cognition. These white matter abnormalities were especially predominant in parts of the brain involved in cognitive function. Unexpectedly, no differences were seen in MS lesions detected with conventional MRI, or in gray matter volumes of particular brain regions in people with cognitive impairment vs. people without cognitive impairment.
The researchers observed differences in the brains of people with MS who had cognitive problems versus those who did not, adding to a growing body of evidence outlining the biological basis for cognitive symptoms in MS. The study also found that loss of nerve-insulating myelin, more than the loss of nerve cells, may be a key factor in cognitive problems, and supports the approach of using DTI as one way to measure the impact of potential therapies aimed at protecting the nervous system from MS damage.
Additional research, now in progress, is needed to determine how sensitive DTI is to changes in nervous system tissue integrity over time and its relation to cognitive changes in MS.