AQP4 and narcolepsy: NMOsd with AQP4-IgG can be diagnosed when one of the six typical core syndromes is recognised (optic neuritis, acute myelitis, area postrema syndrome, acute brainstem syndrome, symptomatic narcolepsy or acute diencephalic clinical syndrome with NMOsd-typical diencephalic MRI lesions, symptomatic cerebral syndrome with NMOsd-typical brain lesions); and is associated with seropositivity for AQP4-IgG detected by the best available method when alternative diagnoses are excluded.