Trans-Synaptic Axonal Degeneration in the Visual Pathway in Multiple Sclerosis

Objective: To evaluate the association between the damage to the anterior and posterior visual pathway as evidence of the presence of retrograde and anterograde trans-synaptic degeneration in multiple sclerosis (MS). Methods: We performed a longitudinal evaluation on a cohort of 100 patients with MS, acquiring retinal optical coherence tomography to measure anterior visual pathway damage (peripapillary retinal nerve fiber layer [RNFL] thickness and macular volume) and 3T brain magnetic resonance imaging (MRI) for posterior visual pathway damage (volumetry and spectroscopy of visual cortex, lesion volume within optic radiations) at inclusion and after 1 year. Freesurfer and SPM8 software was used for MRI analysis. We evaluated the relationships between the damage in the anterior and posterior visual pathway by voxel-based morphometry (VBM), multiple linear regressions, and general linear models. Results: VBM analysis showed that RNFL thinning was specifically associated with atrophy of the visual cortex and with lesions in optic radiations at study inclusion (p < 0.05). Visual cortex volume (beta = +0.601, 95% confidence interval [CI] = +0.04 to +1.16), N-acetyl aspartate in visual cortex (beta = +1.075, 95% CI = +0.190 to +1.961), and lesion volume within optic radiations (beta = -2.551, 95% CI = -3.910 to -1.192) significantly influenced average RNFL thinning at study inclusion independently of other confounders, especially optic neuritis (ON). The model indicates that a decrease of 1cm(3) in visual cortex volume predicts a reduction of 0.6lm in RNFL thickness. This association was also observed after 1 year of follow-up. Patients with severe prior ON (adjusted difference = -3.01, 95% CI = -5.08 to -0.95) and mild prior ON (adjusted difference = -1.03, 95% CI = -3.02 to +0.95) had a lower adjusted mean visual cortex volume than patients without ON. Interpretation: Our results suggest the presence of trans-synaptic degeneration as a contributor to chronic axon damage in MS.