MOG and myeloid sarcoma: Jarius et al illustrate this by calculating that, assuming a hypothetical prevalence of 1% of MOGAD among cases currently diagnosed with MS, screening all MS cases with a hypothetical MOG-IgG assay with 100% sensitivity and 99% specificity would produce 1000 true positive results alongside 990 false positive results, which would be unacceptable.11Therefore, MOG-IgG testing should be reserved for patients with a compatible clinical and radiological picture and low positive results should be interpreted with caution.8