Amyotrophic lateral sclerosis (ALS) is a sporadic motor neuron disorder characterized by the progressive degeneration of both upper and lower motor neurons. Patients with ALS have progressive muscle weakness and atrophy, muscle spasticity, and increasing difficulties swallowing and breathing. Primary lateral sclerosis (PLS) involves the progressive dysfunction only of the upper motor neurons and is characterized by progressive spasticity and weakening of voluntary muscles. While it was originally believed that cognitive functions in ALS and primary lateral sclerosis patients were spared, it is now known that some cognitive impairment, particularly executive dysfunction, may be present in up to 30 percent of (ALS) patients. In this study, we used different MRI imaging techniques such as diffusion tensor imaging (DTI) to examine whether differences in gray matter volume were present between ALS and primary lateral sclerosis. In addition, we tested the hypothesis that differences in cognitive function would correlate to DTI diffusion properties in white matter association tracts.
Structural and DTI imaging as well as neuropsychological testing was carried out on 13 patients with amyotrophic lateral sclerosis, 15 patients with primary lateral sclerosis, and 15 age-matched healthy controls. To quantitatively analyze the diffusion measures from DTI imaging, white matter atlases were created for each subject and then fitted to a standard template. A voxel-based morphometry (VBM) analysis was performed to assess volumetric differences between patient groups and healthy controls.
Changes in diffusion properties in extra-motor regions including association and limbic fiber tracts correlated with decreased scores in tests of executive function as well as memory and general cognitive function. Volumetric changes as seen from the structural analysis of the gray matter were present in motor regions in primary lateral sclerosis and in the cingulate gyrus in ALS which supports results from previous studies.
This study shows that different diffusion properties can provide useful information in assessing white matter abnormalities in both patients with ALS and primary lateral sclerosis and these differences in extra-motor areas can be associated with cognitive functions in both patient groups. In addition, differences found in volumetric analysis of gray matter of ALS and primary lateral sclerosis patients should be viewed with caution. Also, because DTI studies the random motion of water, any relationship between DTI findings and cognitive functions should be carefully interpreted. Further studies are needed to confirm these findings.
Last updated December 14, 2012