The dilated veins surrounding the cord in multiple sclerosis suggest elevated pressure and obstruction of the glymphatic system

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

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.

A Lumped Parameter Model Suggests That Infusion Studies Overestimate the Cerebrospinal Fluid Outflow Resistance in Normal Pressure Hydrocephalus

BACKGROUND/OBJECTIVES

Cerebrospinal infusion studies indicate that cerebrospinal fluid outflow resistance (Rout) is elevated in normal pressure hydrocephalus (NPH). These studies assume that the cerebrospinal formation rate (CSFfr) does not vary during the infusion. If the CSFfr were to increase during the infusion then the Rout would be overestimated. Previous estimates of the CSFfr in NPH have suggested a low figure. More recent estimates of the CSFfr suggest that it is increased, indicating it probably varies with measurement technique. This would bring the estimation of Rout into doubt. A previous paper using a lumped parameter model suggested the CSFfr could vary with the capillary transmural pressure (TMP) in this disease, suggesting a possible solution to this problem. The current study investigates the possibility that the intracranial pressure manipulation occurring during an infusion study may vary the capillary TMP and CSFfr.

METHODS

A lumped parameter model previously developed to describe the hydrodynamics of NPH was modified to investigate the effect of CSF pressure manipulation during infusion studies and to describe how the CSFfr could vary depending on the technique used.

RESULTS

The model indicates the capillary transmural pressure is normal in NPH and increases during an infusion study. CSF drainage at the end of an infusion study similarly increases the capillary TMP and, presumably, the CSFfr by increasing the interstitial fluid production.

CONCLUSIONS

The model suggests that infusion studies and draining CSF increases the CSFfr in NPH compared to earlier techniques. Allowing for an increase in the CSFfr suggests that infusion overestimates the Rout by between 23 and 33%. This study indicates that further research may be required into the utility and accuracy of infusion studies and their ability to diagnose NPH.

Ginkgolide B can alleviate spinal cord glymphatic system dysfunction and provide neuroprotection in painful diabetic neuropathy rats by inhibiting matrix metalloproteinase-9

The glymphatic system plays a crucial role in maintaining optimal central nervous system (CNS) function by facilitating the removal of metabolic wastes. Aquaporin-4 (AQP4) protein, predominantly located on astrocyte end-feet, is a key pathway for metabolic waste excretion. β-Dystroglycan (β-DG) can anchor AQP4 protein to the end-feet membrane of astrocytes and can be cleaved by matrix metalloproteinase (MMP)-9 protein. Studies have demonstrated that hyperglycemia upregulates MMP-9 expression in the nervous system, leading to neuropathic pain. Ginkgolide B (GB) exerts an inhibitory effect on the MMP-9 protein. In this study, we investigated whether inhibition of MMP-9-mediated β-DG cleavage by GB is involved in the regulation of AQP4 polarity within the glymphatic system in painful diabetic neuropathy (PDN) and exerts neuroprotective effects. The PDN model was established by injecting streptozotocin (STZ). Functional changes in the glymphatic system were observed using magnetic resonance imaging (MRI). The paw withdrawal threshold (PWT) was measured to assess mechanical allodynia. The protein expressions of MMP-9, β-DG, and AQP4 were detected by Western blotting and immunofluorescence. Our findings revealed significant decreases in the efficiency of contrast agent clearance within the spinal glymphatic system of the rats, accompanied by decreased PWT, increased MMP-9 protein expression, decreased β-DG protein expression, and loss of AQP4 polarity. Notably, GB treatment demonstrated the capacity to ameliorate spinal cord glymphatic function by modulating AQP4 polarity through MMP-9 inhibition, offering a promising therapeutic avenue for PDN.