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Differentiation between dysmyelination and demyelination using magnetic resonance diffusional anisotropy
1Department of Pediatrics, Faculty of Medicine, Osaka University, Japan.
Abstract:
Using magnetic resonance (MR) diffusion-weighted method, we examined the optic and the trigeminal nerves of jimpy and twitcher mice, considered to be animal models of Pelizaeus-Merzbacher disease, hypomyelination disorder, and Krabbe disease, demyelination disorder, respectively. In jimpy mice, diffusional anisotropy of optic nerve did not show a significant difference compared to age-matched control mice, suggesting that diffusional anisotropy does exist in absence of multiple layers of myelin sheath. In twitcher mice, diffusional anisotropy was attenuated remarkably in the optic and trigeminal nerves. Loss of axonal straightness on longitudinal section confirmed by electron microscopy appeared to be the principal explanation for it. It is further suggested that this MR diffusion-weighted imaging method enables us to differentiate hypomyelination from demyelination in vivo.
Insights
Magnetic resonance diffusion-weighted imaging differentiates hypomyelination from demyelination. This method revealed intact diffusion anisotropy in hypomyelination (jimpy mice) but reduced anisotropy in demyelination (twitcher mice).
Area of Science:
- Neuroscience
- Medical Imaging
- Biochemistry
Background:
- Pelizaeus-Merzbacher disease (hypomyelination) and Krabbe disease (demyelination) are severe neurological disorders.
- Animal models, jimpy and twitcher mice, are crucial for studying these conditions.
- Current diagnostic methods may not always distinguish between hypomyelination and demyelination in vivo.
Purpose of the Study:
- To investigate the utility of magnetic resonance (MR) diffusion-weighted imaging (DWI) in differentiating hypomyelination from demyelination.
- To examine diffusion properties of the optic and trigeminal nerves in mouse models of these disorders.
Main Methods:
- Utilized MR diffusion-weighted imaging to assess optic and trigeminal nerves in jimpy (hypomyelination) and twitcher (demyelination) mice.
- Compared diffusion parameters in affected nerves against age-matched control mice.
- Corroborated findings with electron microscopy to assess axonal integrity.
Main Results:
- Jimpy mice showed no significant difference in optic nerve diffusional anisotropy compared to controls, indicating anisotropy exists without extensive myelin.
- Twitcher mice exhibited markedly attenuated diffusional anisotropy in both optic and trigeminal nerves.
- Electron microscopy confirmed loss of axonal straightness as a primary cause for anisotropy reduction in twitcher mice.
Conclusions:
- MR diffusion-weighted imaging can differentiate between hypomyelination and demyelination in vivo.
- Diffusional anisotropy is preserved in hypomyelination but significantly reduced in demyelination.
- Axonal integrity plays a critical role in maintaining diffusion anisotropy in myelinated nerves.