The prevalence of intrathecal IgM was lower in CIS than in RRMS patients also when assessed as LS-OCMBs (23.7% versus 38.9%, p < 0.00001), OCMBs (33.0% versus 48.5%, p < 0.00001), and IgMLoc (18.8% versus 31.3%, p < 0.00001). Here, CD40LG is linked to in situ carcinoma.