Neuromyelitis optica (NMO) consists of separate attacks of acute optic neuritis (bilateral or unilateral) and myelitis. In contrast to MS, the brain MRI is typically, but not always, normal. A focal enhancing region of swelling and cavitation, extending over three or more spinal cord segments, is typically seen on spinal MRI. A highly specific autoantibody directed against the water channel aquaporin-4 is present in the sera of two-thirds of pts with a clinical diagnosis of NMO. Acute attacks are usually treated with high-dose glucocorticoids as for MS exacerbations. Plasma exchange has also been used empirically for acute episodes that fail to respond to glucocorticoids. Prophylaxis against relapses can be achieved with mycophenolate mofetil, rituximab, or a combination of glucocorticoids plus azathioprine.

Acute MS (Marburg's variant) is a fulminant demyelinating process that progresses to death within 1-2 years. No controlled trials of therapy exist; high-dose glucocorticoids, plasma exchange, and cyclophosphamide have been tried, with uncertain benefit.