As in MS and MOG-EM/MOGAD, ON in NMOSD was associated with prolonged P100 latencies caused by demyelination both in AQP4-IgG-positive and in mixed, AQP4-IgG-positive and AQP4-IgG-negative cohorts [84, 178, 179]. Here, AQP4 is linked to erythema multiforme.