Connecting white matter injury and thalamic atrophy in clinically isolated syndromes

Lesion probability mapping to explain clinical deficits and cognitive performance in multiple sclerosis

BACKGROUND

Lesion dissemination in time and space represents a key feature and diagnostic marker of multiple sclerosis (MS). The correlation between magnetic resonance imaging (MRI) lesion load and disability is only modest, however. Strategic lesion location might at least partially account for this 'clinico-radiologic paradox'.

OBJECTIVES

Here we used a non-parametric permutation-based approach to map lesion location probability based on MS lesions identified on T2-weighted MRI. We studied 121 patients with clinically isolated syndrome, relapsing-remitting or secondary progressive MS and correlated these maps to assessments of neurologic and cognitive functions.

RESULTS

The Expanded Disability Status Scale correlated with bilateral periventricular lesion location (LL), and sensory and coordination functional system deficits correlated with lesion accumulation in distinct anatomically plausible regions, i.e. thalamus and middle cerebellar peduncule. Regarding cognitive performance, decreased verbal fluency correlated with left parietal LL comprising the putative superior longitudinal fascicle. Delayed spatial recall correlated with _amygdalar, _left frontal and parietal LL. Delayed selective reminding correlated with bilateral frontal and temporal LL. However, only part of the spectrum of cognitive and neurological problems encountered in our cohort could be explained by specific lesion location.

CONCLUSIONS

Lesion probability mapping supports the association of specific lesion locations with symptom development in MS, but only to limited extent.

Feasibility of prefronto-caudate pathway tractography using high resolution diffusion tensor tractography data at 3T

Mapping the human brain frontostriatal pathways using noninvasive diffusion tensor imaging (DTI) has been hampered by the inadequate imaging sensitivity, poor spatial resolution, lower tensor anisotropy within gray matter, increased partial volume averaging effects and poor signal-to-noise ratio. We investigated for the first time the utility of high spatial resolution DTI-based fiber-tractography using the fiber assignment by continuous tracking (FACT) to reconstruct and quantify bilaterally the prefronto-caudo-thalamic connections within the human brain at 3T. Five healthy right-handed men (age range 24-37 years) were studied. We traced the anterior thalamic radiation and prefronto-caudo-thalamic pathways bilaterally and measured the volume of each tract and the corresponding diffusion tensor metrics in all subjects. The anterior thalamic radiation tract volume and corresponding fractional anisotropy (FA) were significantly larger bilaterally than prefronto-caudate pathway, whereas the mean diffusivity (D(av)) values were similar (p>0.7). For both anterior thalamic radiation and prefronto-caudate pathway the tract volume and corresponding DTI metrics (FA, D(av)) were not significantly different between the two hemispheres (p>0.2). Our DTI acquisition protocol and analysis permitted the reconstruction of the connectivity of the caudate with the thalamus as well as with the prefrontal cortex and allowed tracking of the whole trajectory of the prefronto-caudo-thalamic pathway.

Multiparametric MR investigation of the motor pyramidal system in patients with 'truly benign' multiple sclerosis

One possible explanation for the mismatch between tissue damage and preservation of neurological functions in patients with benign multiple sclerosis (BMS) is that the pathophysiology differs from that occurring in other multiple sclerosis (MS) phenotypes. The objective of this study was to identify pathologically specific patterns of tissue integrity/damage characteristics of patients with BMS, and markers of potential prognostic value. The pyramidal system was investigated in 10 BMS patients and 20 controls using voxel-based morphometry to assess grey matter (GM) atrophy, and diffusion tractography and quantitative magnetization transfer to quantify the microstructural damage in the corticospinal tracts (CSTs). Widespread reductions in GM volume were found in patients compared with controls, including the primary motor cortex. A significant decrease was observed in the mean macromolecular pool ratio (F) of both CSTs, with no fractional anisotropy (FA) change. GM volume of the primary motor areas was associated with clinical scores but not with the CST parameters. The mismatch between F and FA suggests the presence of extensive demyelination in the CSTs of patients with BMS, in the absence of axonal damage. The lack of correlation with GM volume indicates a complex interaction between disruptive and reparative mechanisms in BMS.