In patients with NMO, attacks of ON can be bilateral and produce severe visual loss (uncommon in MS); myelitis can be severe and transverse (rare in MS) and is typically longitudinally extensive involving three or more contiguous veebral segments. Also in contrast to MS, progressive symptoms typically do not occur in NMO. The brain MRI was earlier thought to be normal in NMO, but it is now recognized that in many cases brain lesions are present, including areas of nonspecific signal change as well as lesions associated with specific syndromes such as the hypothalamus causing an endocrinopathy; the area postrema in the lower medulla presenting as intractable hiccoughs or vomiting; or the cerebral hemispheres producing focal symptoms, encephalopathy, or seizures. Large MRI lesions in the cerebral hemispheres can be asymptomatic, sometimes have a "cloud-like" appearance and, unlike MS lesions, are often not destructive, and can resolve completely. NMO is an autoimmune disease associated with a highly specific autoantibody directed against aquaporin-4 (AQP4) that is present in the sera of ~70% of patients with a clinical diagnosis of NMO. AQP4 is localized to the foot Ref Harrison 20th edition page 3202