A

1,175

18 Months

18 Months

Figure 14 Average mean diffusivity (A) and mean diffusivity histogram peak height (B) of gray matter during an 18-month follow-up study of patients with relapsing-remitting multiple sclerosis where diffusion-weighted magnetic resonance imaging was obtained at baseline and then every three months. Vertical bars represent 95% confidence intervals. Continuous lines represent the linear trends for each variable, as resulting from the respective time trend analyses. Mean diffusivity is expressed in mm2/sec.

Figure 14 Average mean diffusivity (A) and mean diffusivity histogram peak height (B) of gray matter during an 18-month follow-up study of patients with relapsing-remitting multiple sclerosis where diffusion-weighted magnetic resonance imaging was obtained at baseline and then every three months. Vertical bars represent 95% confidence intervals. Continuous lines represent the linear trends for each variable, as resulting from the respective time trend analyses. Mean diffusivity is expressed in mm2/sec.

NAA and increased ADC have also been demonstrated in the thalamus of SPMS (199,200) and RRMS (200,201) patients. As shown for cortical changes, deep GM abnormalities are also more pronounced in SPMS than in RRMS patients (200).

Significant correlations have been reported between MT MRI and DW MRI changes and T2-lesion volume (172,188,189,192). This fits with the notion that at least part of the GM pathology in MS is secondary to retrograde degeneration of fibers traversing WM lesions.

A precise and accurate quantification of GM damage might help to explain some of the clinical manifestations of MS, such as cognitive impairment, and might contribute to increase the strength of the correlation between clinical and MRI findings. Recent studies have indeed found a correlation between the severity of cognitive impairment, and the degree of MTR (180) and MD (177) changes in the GM of MS patients. In addition, GM MTR metrics have been shown to correlate with the severity of clinical disability in patients with RRMS (189) and PPMS (191). Disappointingly, no correlation has been demonstrated between the extent of GM pathology, measured using MT MRI and DW MRI, and severity of fatigue (202).

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