AQP4 and neuromyelitis optica: Furthermore, LETM lesions or lesions of the area postrema is one of the definitive features of NMO [1]; it has been reported that the size of the lesion, especially in the spinal cord, were quite small at each perivascular sites in most previous studies using pooled purified anti-AQP4 antibodies [19, 21, 22, 27], which is distinct from the diffuse extensive lesions observed in NMO.