Variants of multiple sclerosis.

The classic multiple sclerosis variants including Devic's neuromyelitis optica (NMO), Balo's concentric Sclerosis, Schilder's disease, and Marburg MS are both interesting and instructive from a disease pathophysiology perspective. Although rare, the variants are important as they often arise in the differential diagnosis for severe, acute demyelinating disease, including MS and acute disseminated encephalomyelitis. In the case of NMO, an originally unsuspected and entirely new pathophysiology based on water channels has been described, only after the recent original description of the more specific diagnostic test for NMO based on serum immunoglobulin.