<h3>Objective:</h3> To develop a method for quantifying retrograde trans-synaptic degeneration (rTSD) in multiple sclerosis (MS) and investigate its association with demographic characteristics and visual function. <h3>Background:</h3> Neurodegeneration occurs early in MS, contributes to irreversible clinical disability, and is poorly mitigated by currently available treatments. rTSD is a phenomenon in which injury to one neuroaxonal unit propagates retrogradely, amplifying neuronal loss from MS lesions. There are no effective ways of quantifying rTSD in the visual pathway and its impact on visual function has not been elucidated. <h3>Design/Methods:</h3> In this cross-sectional single-center study, patients with MS (pwMS) and non-MS controls underwent clinical, standard automated perimetry and optical coherence tomography assessments. Using customized retinal layer segmentation in nasal and temporal hemimacular sectors, we developed an rTSD-index, which compares ganglion cell hemimacular projections corresponding to each cerebral hemisphere, with positive values reflecting right-hemisphere driven rTSD and vice versa, and absolute rTSD-index (ArTSD) values indicating severity. <h3>Results:</h3> A total of 79 pwMS and 23 non-MS controls were included (average age 45±13 and 37±14, 67% and 61% female, respectively). On average, pwMS had higher ArTSD values (mean difference 1.5, p=0.02). Evidence of rTSD was detected in 13/79 (16%) pwMS and 0/23 non-MS controls at an ArTSD threshold of 3.5. In pwMS, longer disease duration was associated with increased ArTSD severity (β=0.9 for each decade of increased disease duration, p=0.03). For each 1 point increase in ArTSD value, there was on average a 0.1 dB worsening in corresponding visual hemifield function after excluding subjects with optic neuritis history (p=0.02). <h3>Conclusions:</h3> rTSD-index is a novel method to quantify rTSD of the visual pathway in MS, which occurs in 1 out of 6 pwMS, is associated with longer disease duration and subclinical visual field defects. Future studies investigating its association with clinical disability, MRI findings, and methods to mitigate it are needed. <b>Disclosure:</b> Mr. Manukyan has nothing to disclose. Miss Zabala has nothing to disclose. Ms. Locke has nothing to disclose. Dr. Guerrero has nothing to disclose. Dr. Kaisey has received personal compensation in the range of $500-$4,999 for serving on a Scientific Advisory or Data Safety Monitoring board for Novartis. Dr. Kaisey has received personal compensation in the range of $5,000-$9,999 for serving on a Speakers Bureau for Biogen. Dr. Kaisey has received personal compensation in the range of $5,000-$9,999 for serving on a Speakers Bureau for Genentech. Dr. Kaisey has received personal compensation in the range of $5,000-$9,999 for serving as an Expert Witness for Eichhorn & Eichhorn, LLP. The institution of Dr. Kaisey has received research support from NMSS. The institution of Dr. Kaisey has received research support from Race to Erase MS. Dr. Khodabakhsh has received personal compensation in the range of $500-$4,999 for serving as a Consultant for Bausch and Lomb. Dr. Khodabakhsh has received personal compensation in the range of $500-$4,999 for serving as a Consultant for Johnson and Johnson. Dr. Khodabakhsh has received personal compensation in the range of $500-$4,999 for serving on a Scientific Advisory or Data Safety Monitoring board for Bausch and Lomb. Dr. Khodabakhsh has received personal compensation in the range of $5,000-$9,999 for serving on a Speakers Bureau for Bausch and Lomb. The institution of Dr. Sicotte has received research support from Biogen. The institution of Dr. Sicotte has received research support from PCORI. The institution of Dr. Sicotte has received research support from NIH. The institution of Dr. Sicotte has received research support from NMSS. Dr. Sicotte has a non-compensated relationship as a National Medical Advisory Committee Chair with National MS Society that is relevant to AAN interests or activities. The institution of Dr. Sati has received research support from National Multiple Sclerosis Society. The institution of Dr. Sati has received research support from National Institutes of Health. Dr. Sati has received publishing royalties from a publication relating to health care. The institution of Dr. Al-Louzi has received research support from the National Multiple Sclerosis Society and American Brain Foundation.
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