Spatial distribution of multiple sclerosis iron rim lesions and their impact on disability

Imaging chronic active lesions in multiple sclerosis: a consensus statement

Chronic active lesions (CAL) are an important manifestation of chronic inflammation in multiple sclerosis and have implications for non-relapsing biological progression. In recent years, the discovery of innovative MRI and PET-derived biomarkers has made it possible to detect CAL, and to some extent quantify them, in the brain of persons with multiple sclerosis, in vivo. Paramagnetic rim lesions on susceptibility-sensitive MRI sequences, MRI-defined slowly expanding lesions on T1-weighted and T2-weighted scans, and 18-kDa translocator protein-positive lesions on PET are promising candidate biomarkers of CAL. While partially overlapping, these biomarkers do not have equivalent sensitivity and specificity to histopathological CAL. Standardization in the use of available imaging measures for CAL identification, quantification and monitoring is lacking. To fast-forward clinical translation of CAL, the North American Imaging in Multiple Sclerosis Cooperative developed a consensus statement, which provides guidance for the radiological definition and measurement of CAL. The proposed manuscript presents this consensus statement, summarizes the multistep process leading to it, and identifies the remaining major gaps in knowledge.

Iron scavenging and myeloid cell polarization

Myeloid cells that populate all human organs and blood are a versatile class of innate immune cells. They are crucial for sensing and regulating processes as diverse as tissue homeostasis and inflammation and are frequently characterized by their roles in either regulating or promoting inflammation. Recent studies in cultured cells and mouse models highlight the role of iron in skewing the functional properties of myeloid cells in tissue damage and repair. Here, we review certain emerging concepts on how iron influences and determines myeloid cell polarization in the context of its uptake, storage, and metabolism, including in conditions such as multiple sclerosis (MS), sickle cell disease, and tumors.

Paramagnetic rim lesions predict greater long-term relapse rates and clinical progression over 10 years

BACKGROUND

Paramagnetic rim lesions (PRLs) have been linked to higher clinical disease severity and relapse frequency. However, it remains unclear whether PRLs predict future, long-term disease progression.

OBJECTIVES

The study aimed to assess whether baseline PRLs were associated with subsequent long-term (10 years) Expanded Disability Status Scale (EDSS) increase and relapse frequency and, if so, whether PRL-associated EDSS increase was mediated by relapse.

METHODS

This retrospective analysis included 172 people with multiple sclerosis (pwMS) with 1868 yearly clinical visits over a mean follow-up time of 10.2 years. 3T magnetic resonance imaging (MRI) was acquired at baseline and PRLs were assessed on quantitative susceptibility mapping (QSM) images. The associations between PRLs, relapse, and rate of EDSS change were assessed using linear models.

RESULTS

PRL+ pwMS had greater overall annual relapse rate (β = 0.068; p = 0.010), three times greater overall odds of relapse (exp(β) = 3.472; p = 0.009), and greater rate of yearly EDSS change (β = 0.045; p = 0.010) than PRL- pwMS. Greater PRL number was associated with greater odds of at least one progression independent of relapse activity (PIRA) episode over follow-up (exp(β) = 1.171, p = 0.009). Mediation analysis showed that the association between PRL presence (yes/no) and EDSS increase was 96.7% independent of relapse number.

CONCLUSION

PRLs are a marker of aggressive ongoing disease inflammatory activity, including more frequent future clinical relapses and greater long-term, relapse-independent disability progression.

Iron in multiple sclerosis - Neuropathology, immunology, and real-world considerations

Iron is an essential element involved in a multitude of bodily processes. It is tightly regulated, as elevated deposition in tissues is associated with diseases such as multiple sclerosis (MS). Iron accumulation in the central nervous system (CNS) of MS patients is linked to neurotoxicity through mechanisms including oxidative stress, glutamate excitotoxicity, misfolding of proteins, and ferroptosis. In the past decade, the combination of MRI and histopathology has enhanced our understanding of iron deposition in MS pathophysiology, including in the pro-inflammatory and neurotoxicity of iron-laden rims of chronic active lesions. In this regard, iron accumulation may not only have an impact on different CNS-resident cells but may also promote the innate and adaptive immune dysfunctions in MS. Although there are discordant results, most studies indicate lower levels of iron but higher amounts of the iron storage molecule ferritin in the circulation of people with MS. Considering the importance of iron, there is a need for evidence-guided recommendation for dietary intake in people living with MS. Potential novel therapeutic approaches include the regulation of iron levels using next generation iron chelators, as well as therapies to interfere with toxic consequences of iron overload including antioxidants in MS.

Multiple sclerosis iron rim lesions are linked to impaired cervical spinal cord integrity using the T1/T2-weighted ratio

BACKGROUND AND PURPOSE

In multiple sclerosis (MS), iron rim lesions (IRLs) are characterized by pronounced tissue matrix damage. The T1/T2-weighted (T1/T2w) ratio represents a postprocessing MRI approach to investigate tissue integrity, but studies investigating spinal cord pathology are missing until now. The aim of this study was to characterize tissue integrity using the T1/T2w ratio in lesions and the normal-appearing white and gray matter (NAWM, NAGM) in the spinal cord and brain in MS patients with and without brain IRLs.

METHODS

Forty MS patients (20 patients with at least one brain IRL and 20 age- and sex-matched patients without IRLs) were included. Normalized cross-sectional area (nCSA) of the upper cervical cord was calculated in addition to T1/T2w values and standard brain and spinal cord MRI parameters.

RESULTS

Patients with IRLs had higher disability scores, a smaller nCSA, and a higher cervical T2 lesion volume. T1/T2w values of brain IRLs were significantly lower compared to non-IRLs (p < .001). Furthermore, T1/T2w values of lesions were significantly lower compared to the NAGM and NAWM, both in the brain and the spinal cord (p < .05 for all comparisons). T1/T2w values of the NAGM and NAWM in the brain and spinal cord did not statistically differ between the IRL group and the non-IRL group.

CONCLUSION

IRLs constitute an imaging marker of disease severity. T1/T2w ratio maps represent an interesting technique to capture diffuse tissue properties. Calculation of T1/T2w ratio maps of the spinal cord might provide additional insights into the pathophysiological processes of MS.

Cerebrospinal fluid–related tissue damage in multiple sclerosis patients with iron rim lesions

Background:

In multiple sclerosis (MS), iron rim lesions (IRLs) are associated with pronounced tissue damage, higher disease severity and have been suggested as an imaging marker of chronic active inflammation behind the blood–brain barrier indicating progression. Furthermore, chronic intrathecal compartmentalized inflammation has been suggested to be a mediator of a cerebrospinal fluid (CSF)–related tissue damage.

Objective:

To investigate CSF markers of intrathecal inflammation in patients with at least one IRL compared to patients without IRLs and to investigate tissue damage in lesions and normal-appearing white matter (NAWM) with proximity to CSF spaces.

Methods:

A total of 102 patients (51 with at least 1 IRL and 51 age-/sex-matched patients without IRL) scanned with the same 3T magnetic resonance imaging (MRI) and having CSF analysis data were included.

Results:

Patients with at least one IRL had higher disability scores, higher lesion volumes, lower brain volumes and a higher intrathecal immunoglobulin G (IgG) synthesis. Apparent diffusion coefficient (ADC) values in IRLs were higher compared to non-IRLs. We observed a negative linear correlation of ADC values in all tissue classes and distance to CSF, which was stronger in patients with high IgG quotients.

Conclusion:

IRLs are associated with higher intrathecal IgG synthesis. CSF-mediated intrathecal smouldering inflammation could explain a CSF-related gradient of tissue damage.

Exploring (peri-) lesional and structural connectivity tissue damage through T1/T2-weighted ratio in iron rim multiple sclerosis lesions

OBJECTIVE

In multiple sclerosis (MS), iron rim lesions (IRLs) on magnetic resonance imaging (MRI) are associated with pronounced intralesional tissue damage. The aim of this study was to investigate (peri-)lesional and structural connectivity tissue damage in IRLs compared to non-IRLs.

MATERIAL AND METHODS

MRI was acquired on a 3 T system. Tissue integrity was assessed using the T1/T2-weighted (T1/T2w) ratio. Furthermore, we assessed the impact on structural network connectivity accounting for differences in lesion volumes and T1/T2w values.

RESULTS

Seventy-six patients (38 with at least one IRL and 38 age- and sex-matched patients without IRLs) were included. In the IRL-group, T1/T2w ratios of IRLs were significantly lower compared to non-IRLs (p < 0.05). When comparing the T1/T2w ratios in non-IRLs between the IRL-group and non-IRL group, there was no significant difference (p = 0.887). We observed a centrifugal decrease in microstructural damage from lesions to the perilesional white matter. In the IRL-group, T1/T2w ratios in the perilesional white matter 3-8 mm distant to the lesion were significantly lower in IRLs compared to non-IRLs. We found no significant differences in the amount of network disruption between both lesion types (p = 0.122).

CONCLUSION

T1/T2w represents an interesting candidate to capture a pronounced intra- and perilesional tissue damage of IRLs. However, our preliminary results suggest that a pronounced tissue damage might not result in a higher disruption to structural connectivity networks in IRLs.