Quantitative Susceptibility Mapping More Effective Than Brain Atrophy Imaging in Monitoring MS

David Bai

Multiple sclerosis (MS) is a neurodegenerative disease that progresses and can result in increased disability. Delays in brain atrophy imaging, the current gold standard test for identifying disease progression, to detect patients at a high risk of developing physical disabilities from MS, reinforces the need for better measuring tools. Quantitative susceptibility mapping (QSM) is a recent MRI technique that detects iron concentrations at different areas of the brain.

In their new study of brain iron levels and its association with disability, published in Radiology, Zinvadinov et al hypothesized that susceptibility can help identify disease progression earlier than brain atrophy.
The purpose of this study was to determine if there was a relationship between susceptibility and disability and to validate if QSM is a valid technique to detect disease progression.

Six-hundred patients with MS (452 relapse-remitting, 148 secondary progressive) and 250 healthy patients underwent quantitative MRI imaging to detect susceptibility results in the thalamus and the basal ganglia (caudate, putamen, and globus pallidus). Clinical disability was determined through the Expanded Disability Status Scale.  

Results from this study found that patients with MS had a lower thalamic susceptibility (parts per billion [ppb]–7.5 vs –1.1; P <.001) and a higher susceptibility in basal ganglia, caudate, putamen, and globus pallidus (P <.001) than healthy patients. Compared to relapsing-remitting MS, secondary progressive MS had lower thalamic susceptibility (–10.9 vs –6.4 ppb; P = .011), higher basal ganglia susceptibility (66.7 vs 60.5 ppb; P = .041), but not significantly higher susceptibility in the individual components of the basal ganglia (caudate, putamen, and globus pallidus).

Lower thalamic susceptibility was also associated with longer disease duration (P = .002), higher degree of disability (P = .03), and secondary progressive MS (P = .009). The other significant measure was that higher susceptibility in the globus pallidus was associated with a higher degree of disability (P = .03).

To determine if brain atrophy was the sole reason for the changes in iron concentrations, a voxelwise analysis was done that corrected structural tissue volume in each area of the brain. Even though structural tissue volumes were corrected, patients with MS still had lower thalamic susceptibility and higher basal ganglia, caudate, putamen, and globus pallidus susceptibility compared with healthy patients. Patients with secondary progressive MS also had lower thalamic susceptibility and higher globus pallidus susceptibility than patients with relapsing-remitting MS. The voxelwise analysis speculates that indirect tissue loss may not be the only contributing factor to iron changes, further supporting that iron concentration determined through QSM may be an alternate predictor of disability and disease progression compared with brain atrophy imaging.  

From this study, it was shown that lower susceptibility in the thalamic and higher susceptibility in the basal ganglia was associated with patients with MS and MS disease progression. Although more research needs to be done to further authenticate the role of QSM in detecting disease progression in patients with MS, this study is a valuable starting point that helps identify that susceptibility may become a key defining marker for patients with MS and disease progression. 

Zivadinov R, Tavazzi E, Bergsland N, et al. Brain iron at quantitative MRI is associated with disability in multiple sclerosis [published online July 17, 2018]. Radiology. doi:10.1148/radiol.2018180136.

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