Smouldering Multiple Sclerosis: How Can MRI Help in Its Identification?
With the changing understanding of the etiopathogenesis of multiple sclerosis, several new questions arise. One of them is the question of identifying the progressive phase of the disease. Can magnetic resonance imaging (MRI) help in this regard?
Progression independent of relapses
In some patients with multiple sclerosis (MS), there is a progression of neurological impairment despite the absence of apparent inflammatory activity. This phenomenon is usually identified as “progression independent of relapse activity” (PIRA) or “smouldering MS.”
Smouldering MS is likely present from the onset of the disease, although its quantitative representation changes. In patients with progressive MS, this process is more prevalent. Imaging chronic inflammatory activity manifesting as smouldering lesions of the central nervous system could help in the identification and objectification of progressive MS. This is particularly important given the different management required for patients with this form of the disease.
Smouldering lesions up close
Histopathologically, smouldering lesions are characterized by an inactive center surrounded by a rim of macrophages and microglia containing iron. This correlates with a possible imaging method, specifically the identification of paramagnetic rims in T2-weighted images during MRI examinations. However, this method is not commonly available.
Slowly expanding lesions as a suitable marker?
The authors of a study published in the prestigious journal Multiple Sclerosis utilized a more accessible evaluation option. They searched for slowly expanding, enlarging existing T2 lesions (SEL – slowly expanding lesions) using conventional T2- and T1-weighted images with gadolinium, particularly in 1334 patients with relapsing MS (studies OPERA I and II) and in 555 patients with progressive MS (study ORATORIO).
Patients with progressive MS had a higher average number of SEL compared to those with relapsing MS (6.3 vs. 4.6; p = 0.002) and also a higher volume of these lesions. Slowly expanding lesions did not show gadolinium enhancement, and compared to other lesions, SEL also exhibited lower intensity and a faster decrease in intensity on T1-weighted images.
Conclusion
The question of identifying chronic inflammatory activity, particularly smouldering MS prevalent in progressive forms of the disease, is currently very relevant with the advent of new therapeutic options. The authors of this work present evidence suggesting the potential use of SEL as a promising MRI marker for this process.
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Source:
1. Giovannoni G., Popescu V., Wuerfel J. et al. Smouldering multiple sclerosis: the 'real MS'. Ther Adv Neurol Disord 2022 Jan 25; 15: 17562864211066751, doi: 10.1177/17562864211066751.
2. Elliott C., Wolinsky J. S., Hauser S. L. et al. Slowly expanding/evolving lesions as a magnetic resonance imaging marker of chronic active multiple sclerosis lesions. Mult Scler 2019; 25 (14): 1915−1925, doi: 10.1177/1352458518814117.
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