A study by Japanese researchers published in Neuroradiology found that the myelin in multiple sclerosis (MS) plaques is continuously damaged, more so than axons.
“Myelin imaging with SyMRI and NODDI may be useful for the quantitative assessment of temporal changes in MS plaques,” the authors wrote. They also said that evaluating myelin imaging before and after a certain treatment may help establish imaging biomarkers that could be used to monitor the effect of the treatment.
SyMRI (synthetic magnetic resonance imaging) is an approach that can predict MRI findings at different design parameter settings from at least 3 observed scans. NODDI (neurite orientation dispersion and density imaging) is an approach that uses a 3-compartment model to probe brain tissue microstructure.
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In the present study, researchers led by Shigeki Aoki MD, PhD, used these 2 approaches to test whether myelin is more susceptible to damage over time than axons.
They analyzed 31 patients with MS. Altogether, the patients had 73 newly appeared plaques. The researchers performed a simple linear regression analysis to assess the association between the estimated duration from plaque onset and quantitative MRI metrics.
They found that plaques with a longer estimated time from onset were significantly associated with a lower myelin volume fraction and higher g-ratio. The g-ratio is associated with the velocity of neuron conduction. Lesions with pure demyelination have a high g-ratio, while those with concomitant myelin and axonal loss usually have an unchanged g-ratio.
“These findings suggested that myelin experiences ongoing damage more so than axons in plaques,” the researchers concluded.
Magnetic resonance imaging is used to diagnose MS and follow-up with patients. However, it is nonspecific and does not allow easy assessment of myelin status. The approaches described in this study could be useful for the quantitative assessment of MS plaques over time.
Maekawa T, Hagiwara A, Yokoyama K, et al. Multiple sclerosis plaques may undergo continuous myelin degradation: a cross-sectional study with myelin and axon-related quantitative magnetic resonance imaging metrics. Neuroradiology. Published online August 12, 2021. doi:10.1007/s00234-021-02781-0