Optic nerve as a 5th location in the revised McDonald diagnostic criteria for multiple sclerosis: limitations of OCT in the acute phase.

Background: The updated International Panel's diagnostic criteria for multiple sclerosis (2024 revision of McDonald criteria) have for the first time included the optic nerve as the fifth location for dissemination in space (DIS) criterion. The new requirement consists of evidence of significant retinal asymmetry. However, this can be challenging in the acute phase in absence of optic disc swelling. Here, we have investigated the sensitivity of retinal asymmetry over time, from the acute to the chronic phase of optic neuritis. Methods: This observational study analysed longitudinal optical coherence tomography (OCT) images of 25 patients with optic neuritis and 5 healthy controls. Spectral domain OCT scans were obtained from the macula and optic disc. The peripapillary retinal nerve fibre layer (pRNFL), macular ganglion cell (mGCL) and inner plexiform layers (mIPL) were measured in the acute (≤7 days), subacute (between 1 and 12 weeks) and chronic (>3 months) phase. Results: The OCT measurements showed progressive thinning in pRNFL and mGCIPL layers as the disease progressed. In the acute phase, the sensitivity of the pRNFL was 69% (due to optic disc swelling) and for the mGCPL 27%. In the chronic phase, sensitivity levels increased up to 76% (pRNFL) and 88% (mGCIPL) due to atrophy. Conclusions: A clear understanding of the temporal dynamics of diagnostic findings is important. For OCT, the highest diagnostic sensitivity is achieved for the mGCIPL in the chronic phase. This should be taken into account for timing the test in patients where the acquisition of optic nerve involvement is essential for DIS.