Leptomeningeal involvement is not reported for vitamin B12 deficiency and PML-IRIS, but if this imaging feature is present, Susac’s syndrome, Behçet’s disease, PACNS, ECD and GFAP meningoencephalomyelitis should also be maintained in the differential diagnosis [4, 15, 40, 76]. This evidence concerns the gene GFAP and vitamin B12 deficiency.