Assessing demyelination using myelin water imaging

Myelin water imaging (MWI) is an in vivo MRI technique that images water trapped between the lipid bilayers of myelin, providing a quantitative measure of myelin: the myelin water fraction (MWF). MWI provides evidence for unique anatomical-functional relationships between myelin damage and cognition in MS. It can be used to monitor changes in myelination and its relationship to cognitive worsening or improvement [1].

This study aimed to determine possible anatomical-functional relationships between myelin content and myelin damage location and cognitive performance. A sample of 76 patients with clinically definite MS and 22 age-, sex-, and education-matched healthy controls was used. MS patients had a median EDSS of 3.2 (range 1.0 – 8.5) and median disease duration of 15.5 years (0.3 - 48.0). They all underwent cognitive testing and MRI. Cognitive testing was performed with assessments drawn from cognitive batteries validated for use in MS. Non-parametric permutation testing was used to determine which white matter MWF voxels were associated with cognitive test performance. This resulted in test-specific maps of associated white matter areas (cognitive test-specific white matter regions). For each cognitive test, MS patients were categorised into 1 of 3 groups:

1. cognitively impaired: z-score ≤1.5;


2. mildly impaired: z-score >-1.5 to ≤1;


3. cognitively preserved: z-score ≥1.

In MS patients, significant associations were observed between MWF and performance on the Symbol Digit Modalities Test, Selective Reminding Test, and Controlled Oral Word Association Test. No significant associations were found between myelin measures and cognitive performance in controls. The results showed an anatomical-functional relationship between myelin damage and cognitive performance in MS with unique white matter patterns for different cognitive domains. Mean MWF in cognitive test-specific white matter regions was significantly lower in cognitively impaired versus cognitively preserved MS patients, and was significantly associated with cognitive test performance.

With new MS treatments moving towards remyelination, these findings can be translated to clinical trials. The results suggest that MWI can offer an in vivo biomarker feasible for use in clinical trials investigating cognition, providing a means for monitoring changes in myelination and its association with symptom worsening or improvement.

1. Abel S, et al. Myelin water imaging provides evidence for unique anatomical-functional relationships between myelin damage and different cognitive domains in MS. MSVirtual 2020, Abstract LB1197.

 

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Posted on 25 November, 2020