Quantifying chronic lesion expansion in multiple sclerosis: Exploring imaging markers for longitudinal assessment.

OBJECTIVES: Gradual expansion of multiple sclerosis lesions over time is known to have a significant impact on disease progression. However, accurately quantifying the volume changes in chronic lesions presents challenges due to their slow rate of progression and the need for longitudinal segmentation. Our study addresses this by estimating the expansion of chronic lesions using data collected over a 1-2 year period and exploring imaging markers that do not require longitudinal lesion segmentation. METHODS: Pre- and post-gadolinium 3D-T1, 3D FLAIR and diffusion tensor images were acquired from 42 patients with MS. Lesion expansion, stratified by the severity of tissue damage as measured by mean diffusivity change, was analysed between baseline and 48 months (Progressive Volume/Severity Index, PVSI). Central brain atrophy (CBA) and the degree of tissue loss inside chronic lesions (measured by the change of T1 intensity and mean diffusivity (MD)) were used as surrogate markers. RESULTS: CBA measured after 2 years of follow-up estimated lesion expansion at 4 years with a high degree of accuracy (r = 0.82, p < 0.001, ROC area under the curve 0.92, sensitivity of 94 %, specificity of 85 %). Increased MD within chronic lesions measured over 2 years was strongly associated with future expansion (r = 0.77, p < 0.001, ROC area under the curve 0.87, sensitivity of 81 % and specificity of 81 %). In contrast, change in lesion T1 hypointensity poorly explained future PVSI (best sensitivity and specificity 60 % and 59 % respectively). INTERPRETATION: CBA and, to a lesser extent, the change in MD within chronic MS lesions, measured over a period of 2 years, can provide a reliable and sensitive estimate of the extent and severity of chronic lesion expansion.

Longitudinal enlargement of choroid plexus is associated with chronic lesion expansion and neurodegeneration in RRMS patients.

BACKGROUND AND OBJECTIVE: We explored dynamic changes in the choroid plexus (CP) in patients with relapsing-remitting multiple sclerosis (RRMS) and assessed its relationship with chronic lesion expansion and atrophy in various brain compartments. METHODS: Fifty-seven RRMS patients were annually assessed for a minimum of 48 months with 3D FLAIR, pre- and post-contrast 3D T1 and diffusion-weighted magnetic resonance imaging (MRI). The CP was manually segmented at baseline and last follow-up. RESULTS: The volume of CP significantly increased by 1.4% annually. However, the extent of CP enlargement varied considerably among individuals (ranging from -3.6 to 150.8 mm3 or -0.2% to 6.3%). The magnitude of CP enlargement significantly correlated with central (r = 0.70, p < 0.001) and total brain atrophy (r = -0.57, p < 0.001), white (r = -0.61, p < 0.001) and deep grey matter atrophy (r = -0.60, p < 0.001). Progressive CP enlargement was significantly associated with the volume and extent of chronic lesion expansion (r = 0.60, p < 0.001), but not with the number or volume of new lesions. CONCLUSION: This study provides evidence of progressive CP enlargement in patients with RRMS. Our findings also demonstrate that enlargement of the CP volume is linked to the expansion of chronic lesions and neurodegeneration of periventricular white and grey matter in RRMS patients.

Choroid plexus volume is enlarged in clinically isolated syndrome patients with optic neuritis.

OBJECTIVES: We investigated choroid plexus (CP) volume in patients presenting with optic neuritis (ON) as a clinically isolated syndrome (CIS), compared to a cohort with established relapsing-remitting multiple sclerosis (RRMS) and healthy controls (HCs). METHODS: Three-dimensional (3D) T1, T2-FLAIR and diffusion-weighted sequences were acquired from 44 ON CIS patients at baseline, 1, 3, 6 and 12 months after the onset of ON. Fifty RRMS patients and 50 HCs were also included for comparison. RESULTS: CP volumes was larger in both ON CIS and RRMS groups compared to HCs, but not significantly different between ON CIS and RRMS patients (analysis of covariance (ANCOVA) adjusted for multiple comparisons). Twenty-three ON CIS patients who converted to clinically definite MS (MS) demonstrated CP volume similar to RRMS patients, but significantly larger compared to HCs. In this sub-group, CP volume was not associated with the severity of optic nerve inflammation or long-term axonal loss, not with brain lesion load. A transient increase of CP volume was observed following an occurrence of new MS lesions on brain magnetic resonance imaging (MRI). INTERPRETATION: Enlarged CP can be observed very early in a disease. It transiently reacts to acute inflammation, but not associated with the degree of tissue destruction.

Choroid plexus volume in multiple sclerosis predicts expansion of chronic lesions and brain atrophy.

OBJECTIVES: Recent studies suggested that the expansion of long-standing multiple sclerosis (MS) lesions and an enlargement of choroid plexus may be linked to chronic inflammation and microglial activation. We investigated the potential association between plexus volume and subsequent lesion expansion in patients with relapsing-remitting MS. METHODS: Pre- and post-gadolinium 3D-T1, 3D FLAIR and diffusion tensor images were acquired from 49 patients. Choroid plexus (CP) volume (normalised by Total Intracranial Volume, TIV) and lesion activity were analysed between baseline and 48 months. In addition, plexus volume was measured in 40 healthy controls of similar age and gender. RESULTS: Baseline CP/TIV ratio was significantly larger in RRMS patients compared to normal controls (p < 0.001). CP/TIV ratio remained stable in RRMS patients during follow-up period. There was a strong correlation between baseline CP/TIV ratio and subsequent rate of chronic lesion expansion (p < 0.001), which was stronger in close proximity to CSF. A cut-off of 98 × 10-5 CP/TIV ratio predicted future lesion expansion with a sensitivity of 85% and specificity of 76%. CP/TIV ratio larger than a cut-off was associated with >8-fold increased risk of chronic lesion expansion. Baseline CP/TIV ratio was also associated with change in Mean Diffusivity (MD) inside of chronic lesions. Furthermore, baseline CP/TIV ratio significantly correlated with central brain atrophy. There was, however, no correlation between CP/TIV ratio and volume of new lesions. INTERPRETATION: Our data demonstrate that baseline CP/TIV ratio predicts subsequent expansion of chronic periventricular MS lesions and associated tissue damage within and outside of chronic lesions.

Mechanisms of central brain atrophy in multiple sclerosis.

BACKGROUND: Change in ventricular volume has been suggested as surrogate measure of central brain atrophy (CBA) applicable to the everyday management of multiple sclerosis (MS) patients. OBJECTIVES: We investigated the contribution of inflammatory activity (including the severity of lesional tissue damage) to CBA. METHODS: Fifty patients with relapsing-remitting multiple sclerosis (RRMS) were enrolled. Lesional activity during 4 years of follow-up was analysed using custom-build software, which segmented expanding part of the chronic lesions, new confluent lesions and new free-standing lesions. The degree of lesional tissue damage was assessed by change in mean diffusivity (MD). Volumetric change of lateral ventricles was used to measure CBA. RESULTS: During follow-up, ventricles expanded on average by 12.6% ± 13.7% (mean ± SD). There was a significant increase of total lesion volume, 69.3% of which was due to expansion of chronic lesions. Correlation between volume of combined lesional activity and CBA (r2 = 0.67) increased when lesion volume was adjusted by the degree of tissue damage severity (r2 = 0.81). Regression analysis explained 90% of CBA variability, revealing that chronic lesion expansion was by far the largest contributor to ventricular enlargement. DISCUSSION: CBA is almost entirely explained by the combination of the volume and severity of lesional activity. The expansion of chronic lesions plays a central role in this process.

Long-term Effect of Permanent Demyelination on Axonal Survival in Multiple Sclerosis.

BACKGROUND AND OBJECTIVES: To investigate the long-term effect of permanent demyelination on axonal attrition by examining an association between intereye asymmetry of the multifocal visual evoked potential (mfVEP) latency delay and subsequent thinning of retinal ganglion cell axons in patients with a long-standing history of unilateral optic neuritis (ON). METHODS: Only patients with a significant degree of chronic demyelination (intereye latency asymmetry >5 ms) were included in this study. The level of optic nerve demyelination was estimated at baseline by the latency delay of mfVEP, while the degree of axonal loss was assessed by thinning of the retinal nerve fiber layer (RNFL) thickness between baseline and follow-up visits. Low-contrast visual acuity (LCVA) was also evaluated at baseline and follow-up. Patients were examined twice with an average interval of 6.1 ± 1.4 years. RESULTS: From 85 examined patients with multiple sclerosis, 28 satisfied inclusion criteria. Latency of the mfVEP was delayed, and RNFL thickness was reduced in ON eyes compared with fellow eyes at both visits. There was significant correlation between latency asymmetry and baseline or follow-up intereye RNFL thickness asymmetry. Intereye asymmetry of LCVA at baseline correlated with baseline latency asymmetry of mfVEP and baseline asymmetry of RNFL thickness. Latency of the mfVEP in ON eyes improved slightly during the follow-up period, whereas latency of the fellow eye remained stable. By contrast, RNFL thickness significantly declined in both ON and fellow eyes during the follow-up period. The rate of RNFL thinning in ON eyes, however, was more than 2 times faster compared with the fellow eyes (p < 0.001). Furthermore, baseline latency asymmetry significantly correlated with the rate of RNFL thinning in ON eyes during the follow-up (p < 0.001), explaining almost half of the variability of temporal RNFL progression. For each millisecond of latency delay (i.e., ∼0.5 mm of demyelination along the optic nerve), temporal RNFL thickness was annually reduced by 0.05%. DISCUSSION: Our study provides clear in vivo evidence that chronic demyelination significantly accelerates axonal loss. However, because this process is slow and its effect is mild, long-term monitoring is required to establish and confidently measure the neurodegenerative consequences of demyelination.

The expansion and severity of chronic MS lesions follows a periventricular gradient.

BACKGROUND AND OBJECTIVES: Expansion of chronic lesions in multiple sclerosis (MS) patients and recently described cerebrospinal fluid (CSF)-related gradient of tissue damage are linked to microglial activation. The aim of this study was to investigate whether lesion expansion is associated with proximity to ventricular CSF spaces. METHODS: Pre- and post-gadolinium three-dimensional (3D)-T1, 3D FLAIR and diffusion tensor images were acquired from 36 relapsing-remitting MS (RRMS) patients. Lesional activity was analysed between baseline and 48 months at different distances from the CSF using successive 1 mm thick concentric bands radiating from the ventricles. RESULTS: Voxel-based analysis of the rate of lesion expansion demonstrated a clear periventricular gradient decreasing away from the ventricles. This was particularly apparent when lesions of equal diameter were analysed. Periventricular lesional tissue showed higher degree of tissue destruction at baseline that significantly increased during follow-up in bands close to CSF. This longitudinal change was proportional to degree of lesion expansion. Lesion-wise analysis revealed a gradual, centrifugal decrease in the proportion of expanding lesions from the immediate periventricular zone. DISCUSSION: Our data suggest that chronic white matter lesions in close proximity to the ventricles are more destructive, show a higher degree of expansion at the lesion border and accelerated tissue loss in the lesion core.

Analysis of Multifocal Visual Evoked Potentials Using Artificial Intelligence Algorithms.

Purpose: Clinical trials for remyelination in multiple sclerosis (MS) require an imaging biomarker. The multifocal visual evoked potential (mfVEP) is an accurate technique for measuring axonal conduction; however, it produces large datasets requiring lengthy analysis by human experts to detect measurable responses versus noisy traces. This study aimed to develop a machine-learning approach for the identification of true responses versus noisy traces and the detection of latency peaks in measurable signals. Methods: We obtained 2240 mfVEP traces from 10 MS patients using the VS-1 mfVEP machine, and they were classified by a skilled expert twice with an interval of 1 week. Of these, 2025 (90%) were classified consistently and used for the study. ResNet-50 and VGG16 models were trained and tested to produce three outputs: no signal, up-sloped signal, or down-sloped signal. Each model ran 1000 iterations with a stochastic gradient descent optimizer with a learning rate of 0.0001. Results: ResNet-50 and VGG16 had false-positive rates of 1.7% and 0.6%, respectively, when the testing dataset was analyzed (n = 612). The false-negative rates were 8.2% and 6.5%, respectively, against the same dataset. The latency measurements in the validation and testing cohorts in the study were similar. Conclusions: Our models efficiently analyze mfVEPs with <2% false positives compared with human false positives of <8%. Translational Relevance: mfVEP, a safe neurophysiological technique, analyzed using artificial intelligence, can serve as an efficient biomarker in MS clinical trials and signal latency measurement.

Expansion of chronic MS lesions is associated with an increase of radial diffusivity in periplaque white matter.

BACKGROUND: Expansion of chronic multiple sclerosis (MS) lesion is associated with slow-burning inflammation at lesion rim. However, the underlying mechanisms leading to expansion are not fully understood. OBJECTIVE: To investigate the relationship between diffusivity markers of demyelination and axonal loss in perilesional white matter and lesion expansion in relapsing-remitting MS (RRMS). METHODS: T1, FLAIR and diffusion tensor images were acquired from 30 patients. Novel single-streamline technique was used to estimate diffusivity in lesions, perilesional white matter and normal-appearing white matter (NAWM). RESULTS: Significant association was found between baseline periplaque radial diffusivity (RD) and subsequent lesion expansion. Conversely, periplaque axial diffusivity (AD) did not correlate with lesion growth. Baseline RD (but not AD) in periplaque white matter of expanding lesions was significantly higher compared with non-expanding lesions. Correlation between increase of both RD and AD in the periplaque area during follow-up period and lesion expansion was noticeably stronger for RD. Increase of RD in periplaque area was also much higher compared to AD. There was significant increase of AD and RD in the periplaque area of expanding, but not in non-expanding, lesions. CONCLUSION: Periplaque demyelination is likely to be an initial step in a process of lesion expansion and, as such, potentially represents a suitable target for remyelinating therapies.

Differentiating axonal loss and demyelination in chronic MS lesions: A novel approach using single streamline diffusivity analysis.

We describe a new single-streamline based approach to analyse diffusivity within chronic MS lesions. We used the proposed method to examine diffusivity profiles in 30 patients with relapsing multiple sclerosis and observed a significant increase of both RD and AD within the lesion core (0.38+/-0.09 µm2/ms and 0.30+/-0.12 µm2/ms respectively, p<0.0001 for both) that gradually and symmetrically diminished away from the lesion. T1-hypointensity derived axonal loss correlated highly with ΔAD (r = 0.82, p<0.0001), but moderately with ΔRD (r = 0.60, p<0.0001). Furthermore, the trendline of the ΔAD vs axonal loss intersected both axes at zero indicating close agreement between two measures in assessing the degree of axonal loss. Conversely, the trendline of the ΔRD function demonstrated a high positive value at the zero level of axonal loss, suggesting that even lesions with preserved axonal content exhibit a significant increase of RD. There was also a significant negative correlation between the level of preferential RD increase (ΔRD-ΔAD) in the lesion core and the degree of axonal damage (r = -0.62, p<0.001), indicating that ΔRD dominates in cases with milder axonal loss. Modelling diffusivity changes in the core of chronic MS lesions based on the direct proportionality of ΔAD with axonal loss and the proposed dual nature of ΔRD yielded results that were strikingly similar to the experimental data. Evaluation of lesions in a sizable cohort of MS patients using the proposed method supports the use of ΔAD as a marker of axonal loss; and the notion that demyelination and axonal loss independently contribute to the increase of RD in chronic MS lesions. The work highlights the importance of selecting appropriate patient cohorts for clinical trials of pro-remyelinating and neuroprotective therapeutics.

Expansion of chronic lesions is linked to disease progression in relapsing-remitting multiple sclerosis patients.

BACKGROUND: Slow-burning inflammation is putatively associated with lesion expansion and leads to progressive loss of axons and disability worsening. OBJECTIVE: To investigate the incidence and extent of chronic white matter lesion expansion in relapsing-remitting multiple sclerosis (RRMS) patients and to evaluate its relationship with biomarkers of disease progression. METHODS: Pre- and post-gadolinium T1, fluid-attenuated inversion recovery (FLAIR) and diffusion tensor images were acquired from 33 patients. Lesional activity were analysed between baseline and 48 months using custom-designed software. RESULTS: A total of 569 lesions were identified as chronic at baseline, of which 261 were expanding, 236 were stable and 72 were shrinking. In addition, 139 new lesions (both confluent and free-standing) were observed. Chronic lesion expansion was associated with patient's age and accounted for the bulk (67.3%) of total brain lesion volume increase, while only 32.7% was attributable to new lesion formation. Change in chronic lesion volume correlated with the rate of brain atrophy (r = -0.57, p = 0.001), change of Expanded Disability Status Scale (EDSS; r = 0.38, p = 0.03) and an increase of isotropic diffusivity inside the lesions (r = 0.75, p < 0.001). CONCLUSION: Expansion of chronic lesions in RRMS patients is the primary determinant of increased T2 total lesion load. It significantly contributes to disease progression and partially driving axonal loss inside the lesions and brain damage outside of lesional tissue.