Subclinical anterior optic pathway involvement in early multiple sclerosis and clinically isolated syndromes

Abstract

Optical coherence tomography (OCT) is gaining increasing relevance in the assessment of patients with multiple sclerosis. Converging evidence point to the view that neuro-retinal changes, in eyes without acute optic neuritis, reflect inflammatory and neurodegenerative processes taking place throughout the CNS. The present study aims at exploring the usefulness of OCT as a marker of inflammation and disease burden in the earliest phases of the disease. Thus, a cohort of 150 consecutive patients underwent clinical, neurophysiological and brain MRI assessment as well as lumbar puncture as part of their diagnostic workup for a neurological episode suggestive of inflammatory CNS disorder; among those 32 patients had another previous misdiagnosed episode. For the present study, patients also received a visual pathway assessment (OCT, visual evoked potentials, visual acuity), measurement of CSF inflammatory markers (17 cytokines-chemokines, extracellular vesicles of myeloid origin), and dosage of plasma neurofilaments. Subclinical optic nerve involvement is frequently found in clinically isolated syndromes by visual evoked potentials (19.2%). OCT reveals ganglion cell layer asymmetries in 6.8% of patients; retinal fibre layer asymmetries, despite being more frequent (17.8%), display poor specificity. The presence of subclinical involvement is associated with a greater disease burden. Second, ganglion cell layer thinning reflects the severity of disease involvement even beyond the anterior optic pathway. In fact, the ganglion cell layer in eyes without evidence of subclinical optic involvement is correlated with Expanded Disability Status Scale, low contrast visual acuity, disease duration, brain lesion load, presence of gadolinium enhancing lesions, abnormalities along motor and somatosensory evoked potentials, and frequency of CSF-specific oligoclonal bands. Third, the inner nuclear layer thickens in a post-acute (1.1–3.7 months) phase after a relapse, and this phenomenon is counteracted by steroid treatment. Likewise, a longitudinal analysis on 65 patients shows that this swelling is transient and returns to normal values after 1 year follow-up. Notwithstanding, the clinical, MRI, serological and CSF markers of disease activity considered in the study are strictly associated with one another, but none of them are associated with the inner nuclear layer. Our findings challenge the current hypothesis that the inner nuclear layer is an acute phase marker of inflammatory activity. The present study suggests that instrumental evidence of subclinical optic nerve involvement is associated with a greater disease burden in clinically isolated syndrome. Neuro-retinal changes are present since the earliest phases of the disease and yield important information regarding the neurodegenerative and inflammatory processes occurring in the CNS.

Retinal imaging with optical coherence tomography in multiple sclerosis: novel aspects

“…Furthermore, progressive thinning of the retinal ganglion cell (RGC) and the inner plexiform layer has also been described for relapsing–remitting MS (RRMS) [ 29 ]. This more recent data is consistent with previous literature showing continuous RNFL thinning in CIS and MS patients with and without ON [ 14 , 30 , 31 ]. These findings are consistent with post-mortem analysis of MS patients, showing RNFL, GCL, and INL thinning [ 32 ].…”

“…Within 1 year after the episode, INL levels return to baseline level. INL thickness is therefore discussed as a marker of acute inflammatory activity [ 13 , 14 ]. INL thickening is further associated with the extent of ganglion cell loss after acute ON.…”

“…One assumed mechanism for INL thickening is an accumulation of retinal fluid due to increased vascular permeability within the retina due to an injury of Müller cells. During an ON episode, GCIPL loss occurs, leading to Müller cell activation and INL thickening [ 14 ]. In addition, an effect of ON on outer retinal (OR) layers—including the outer plexiform layer, the outer nuclear layer, and the photoreceptor layer—was shown.…”

“…Furthermore, OCT parameters have also been associated with disability in MS patients. OCT parameters correlating with disability include GCL thickness, pRNFL thickness, total macular volume, and annual atrophy rates of GCIPL and pRNFL [ 13 , 14 , 26 , 52 , 53 ]. GCIPL, pRNFL, and total macular volume are also associated with cognitive performance and executive function [ 54 – 56 ].…”

Characterizing the Retinal Phenotype of the Thy1-h[A30P]α-syn Mouse Model of Parkinson’s Disease

“…Previous studies demonstrated that α-syn triggers neuroinflammation, and that, in turn, inflammation increases α-syn phosphorylation and pathology in synucleinopathies ( Lee et al, 2010 ; Tansey and Goldberg, 2010 ; Ramirez et al, 2017 ; Ferreira and Romero-Ramos, 2018 ). Furthermore, retinal inflammation has been linked to both swelling of the outer retina and ERG deviations, and may therefore underlie -at least in part- the OCT and ERG abnormalities that we observed in the Thy1-h[A30P]α-syn mice ( Mirza and Jampol, 2013 ; Petzold, 2016 ; Pisa et al, 2021 ; Xia et al, 2021 ). Hence, we next investigated macroglia and microglia reactivity and water homeostasis in the retina.…”