Neuromyelitis optica (NMO) has for long been considered as a variant of multiple sclerosis (MS). J de Sèze musters recent data that point to a more fundamental distinction between the two diseases. This new evidence is mainly based on differences in CSF abnormalities which are more severe with MRI cord lesions and the discovery of a highly specific serum antibody called “anti-NMO”. The target of “anti-NMO” has been recently identified as a hydrophilic channel protein called “aquaporin 4”.

These data are compatible with recent clinical series, notably that of El Otmani et al. (Rev Neurol, 2005:161;4) from Morocco. In this issue the Revue Neurologique publishes additional evidence coming from MRI studies (Bonnan et al.).

NMO thus appears distinct from MS and a disorder of humoral immunity, suggesting a vasculitic rather than a demyelinating process. The reason of its affinity for spinal cord and optic nerves remains obscure.

10 references.