The frequent sign of a rare disease or the rare sign of a frequent disease?

We read with high interest the study from Chen et al. (2022) about the role of optical coherence tomography (OCT) at the first episode of acute optic neuritis (ON). Comparing 64 myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD) patients and 50 multiple sclerosis (MS) patients with OCT measurements within two weeks of symptoms onset, they found that MOGAD ON is associated with a larger increase of peri-papillary retinal nerve fibers layer (pRNFL) thickness than MS ON. Moreover, the “optimal” pRNFL cutoff of 118 μm, as determined with Youden's index, provided a sensitivity of 74% and specificity of 82% for discriminating MOGAD from MS.