CHI3L1 and premenstrual tension: Our findings of more contrast-enhancing lesions and higher concentrations of NFL, CHI3L1, IL12p40 and VEGF in patients with IgM OCBs confirm that the presence of IgM OCBs in patients with PMS identifies a subset with increased focal inflammation (Villar et al. 2014), and support further investigation of whether this subset of patients may benefit more from DMTs (Montobbio et al. 2025; Sellebjerg et al. 2017).