Mental Deficit in MS Tied to White Matter Damage

This report is part of a 12-month Clinical Context series.

By John Gever, Senior Editor, MedPage Today

Published: March 07, 2013

Reviewed by Robert Jasmer, MD; Associate Clinical Professor of Medicine, University of California, San Francisco and Dorothy Caputo, MA, BSN, RN, Nurse Planner

Significant differences were seen in sophisticated MRI brain scans between multiple sclerosis (MS) patients with cognitive impairments and those without, apparently unrelated to classic MS lesions, researchers said.

Among impaired patients only, diffusion tensor imaging (DTI) revealed damage to white matter in multiple brain regions, many of which were already known to be important for cognitive function, according to Hanneke Hulst, MSc, of VU University Medical Center in Amsterdam, and colleagues.

Unlike standard MRI scans, diffusion tensor imaging “allows for quantitative measurements of the microstructural integrity of white matter tracts both in the normal-appearing white matter and in areas with MS lesions,” they explained in the March 12 issue of Neurology. “DTI might be a powerful tool when monitoring cognitive impairment in MS.”

Up to 65% of all MS patients develop cognitive impairment, Hulst and colleagues noted. Although previous studies have linked this complication to standard MRI measures such as T1 and T2 lesion volume and overall brain atrophy, these associations do not account for all the variation between patients.

In particular, conventional MRI does not pick up small-scale alterations in white matter, which also could contribute to cognitive problems in MS patients.

To explore the question further, Hulst and colleagues performed conventional MRI and diffusion tensor imaging scans in 55 MS patients and 20 healthy controls. Patients and controls were mostly middle-age (means in the three groups ranged from 46 to 50) and, in line with the distribution of MS in the general population, were mostly female. Disease duration in the patients was about 12 years.

All participants underwent neuropsychological testing in such domains as verbal memory and learning, spatial memory, working memory, semantic memory, and processing speed. Patients with total scores at least two standard deviations below the mean for healthy controls were classed as cognitively impaired.

Hulst and colleagues classified 35 of the patients as cognitively normal and 20 as impaired.

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