AQP4 and myelitis: Myelitis lesions that are longitudinally-extensive (spanning ≥3 contiguous vertebral body segments on T2-weighted images on spine MRI) are also typical of both AQP4 antibodies (Figure 2B4) and MOG autoantibodies and may occur in isolation, accompanied by unilateral or bilateral optic neuritis (neuromyelitis optica), or concomitant brain involvement (65, 66).