Neurodegeneration and Demyelination in the Multiple Sclerosis Spinal Cord: Clinical, Pathological, and 7T MRI Perspectives.

Abstract

Background and objectives: Key findings in people with multiple sclerosis (MS) with progressive motor disability are spinal cord (SC) atrophy signifying irreversible axonal loss and SC demyelinated lesions. This study aimed to identify neurodegenerative changes and assess the clinical impact and pathologic characteristics of SC lesions.

Methods: A cross-sectional study was performed using postmortem cervical cord segments from the Cleveland Clinic MS Rapid Autopsy Program. Inclusion included proximity to our center, absence of transmissible infections, and lack of prolonged hypoxia. In situ MRIs were performed before tissue removal and fixation followed by 7T MRI and immunohistochemistry. Quantitative T2* relaxation times were correlated with myelin, axons, and activated microglia/macrophages (major histocompatibility complex II [MHCII]) using Tukey comparison of means and a linear mixed-effects model; T2* was correlated with clinical disease characteristics using Wilcoxon rank sum.

Results: The study included 40 MS cases (median age 58, female 55%) and 9 controls (median age 69, female 89%). A T2* threshold reliably discriminated demyelination (accuracy 89.7%, sensitivity 95.5%, and specificity 87.0%). Myelin content (95% CI -0.82 to -0.58, estimate -0.70) was the only significant predictor of T2*. T2* hyperintensities within the segments ranged from 0% to 100% (median 33.6, interquartile range 12.9-64.3) with only 57.1% demyelinated. T2*-hyperintense/myelinated regions had increased T2* relaxation time (19.2 ms, 95% CI 9.97-28.4), reduced myelin content (-8.3%, 95% CI -12.1 to -4.4), increased MHCII (3.6%, 95% CI 0.45-6.7), reduced axonal counts (-349.8, 95% CI -565.4 to -134.1), and increased axonal area (2.0 µm², 95% CI 1.0-3.1) compared with normal-appearing MRI regions. These regions occurred adjacent to T2*-hyperintense/demyelinated lesions (periplaque) or along tracts (tract-based). 7T postmortem T2* hyperintensities were subtle on clinical 1.5T axial T2, and only 43% were detected sagittally. T2*-hyperintense/demyelinated lesions correlated with Expanded Disability Status Scale (EDSS) (rho = 0.61, p < 0.0001) and upper cervical cord area (rho = -0.64, p < 0.0001) while T2*-hyperintense/myelinated regions did not.

Discussion: Thresholding 7T T2* postmortem MRI can effectively discriminate demyelinated lesions which correlate with clinical disability and cord atrophy. T2*-hyperintense/myelinated regions exhibit myelin and axonal pathology in periplaque or tract-based distributions suggestive of neurodegeneration. Limitations include sampling of 2-cm of SC across participants making conclusions about proximal and distal pathology difficult.