Diffusion tensor imaging measures of forniceal damage correlate with episodic memory dysfunction in multiple sclerosis patients

• Published in: Multiple sclerosis Vol. 14; p. S210
• Main Authors: Phillips, M, Koenig, KA, Beall, E B, Stone, L, Zimbelman, J, Marrie, R A, Sakaie, KA, Rao, S M, Lowe, MJ
• Format: Journal Article
• Language: English
• Published: 01-09-2008
• ISSN: 1352-4585

Background: An estimated 50% of patients with multiple sclerosis (MS) show cognitive impairment with 30 to 40% of MS patients demonstrating specific deficits in episodic memory. Recent pathologic data demonstrates significant hippocampal demyelination in a subset of patients with MS however, hippocampal white matter changes are difficult to evaluate using DTI due to the structure of the hippocampus. The fornix is the primary efferent of the hippocampus and well suited for evaluation with diffusion tensor imaging (DTI). The fornix has been strongly linked to memory function in a variety of disease processes. Objective: We hypothesize episodic memory dysfunction in MS patients dysfunction will be correlated with forniceal damage demonstrated by DTI changes, specifically, increased in axial diffusivity ( lambda 2) and reduced fractional anisotropy (FA). Methods: Fourteen MS patients with relapsing-remitting MS were studied using DTI and a battery of neuropsychological tests, including the California Verbal Learning Test (CVLT) and Brief Visual Memory Test (BVMT). Diffusion-weighted imaging used 71 non-collinear diffusion-weighting gradients (2.5x2.5x2.5 mm voxels, b=2000 sec/mm2, 8 b=0 acquisitions). Regions of interest were drawn in the cms of the fornix and average values for FA, mean diffusivity, lambda 2 and longitudinal diffusivity ( lambda 1) were measured. Results: Verbal episodic memory dysfunction measured by the CVLT demonstrated a strong correlation with reduced FA (r=0.652, p<0.01) and increased lambda 2 (r=-0.630, p<0.008) within the left fornix. Interestingly, in measures of spatial memory dysfunction, the BVLT demonstrated strong correlation with FA in the right fornix (r=0.766, p<0.001). Conclusions: Findings demonstrated strong correlations between decreased verbal episodic memory and diffusion abnormalities within the left hippocampus. Potential drawbacks to the study include confounding factors related to hippocampal atrophy and possible partial volume averaging of adjacent structures during DTI measurements. Further study using high-resolution DTI is required to confirm these results. Overall findings suggest deficits in episodic memory in MS subjects are strongly correlated with DTI measures of forniceal damage.