Reduced apparent diffusion coefficient in neuromyelitis optica-associated optic neuropathy.

Diffusion-weighted magnetic resonance imaging is a useful tool to differentiate between acute ischemic and demyelinating lesions. In ischemic optic neuropathy the diffusion of water is impaired, but in optic neuritis it usually remains normal. We describe a patient with optic neuritis and aquaporin-4 autoantibodies, in whom imaging revealed prolonged reduction of the apparent diffusion coefficient. Immune-mediated destruction of water channels apparently decreased movement of fluid through the inflamed nerve. Diffusion-weighted imaging may distinguish optic neuritis associated with aquaporin-4 antibodies from the more common form that occurs in conjunction with multiple sclerosis.