AQP4 and transverse myelitis: As encompassed in the term “neuromyelitis optica”, the typical clinical presentation of NMOSD is that of optic neuritis (ON) and/or longitudinally extensive transverse myelitis (LETM) (defined as lesions spanning >3 complete vertebral segments), in the context of seropositivity for AQP4-IgG antibodies [6,21].