A longitudinally extensive cord lesion carries a broad differential diagnosis including parainfectious, autoimmune, demyelinating and vascular conditions. Presence of enhancement, or in lieu of enhancement a proven CSF pleocytosis and increased protein, confirm that this is an inflammatory process.
Relevant findings on brain imaging and clinical features (for example concurrent or recent febrile illness, or evidence of an autoimmune or connective tissue disorder) can then be employed to assist in narrowing the imaging differential diagnosis.
In this case, the distribution of brain lesions corresponds to sites of high expression of aquaporin 4 receptor which points toward NMO, a diagnosis later confirmed by positive NMO autoantibody.
Neuromyelitis optica is a relapsing demyelinating condition that affects spinal cord and optic nerves. Compared to multiple sclerosis, NMO affects an older age group (39 years compared with 29 years), with more pronounced female predominance, and with disproportionate representation from the nonwhite population.
Previously grouped with MS, NMO is now recognised as an autoimmune channelopathy, due to autoantibodies against the aquaporin 4 water channel receptor.
Cord involvement is characterised by longitudinally extensive T2 hyperintense lesions rather than the small peripheral lesions that are typical of MS.
Brain lesions, where present, usually involve subependymal regions and hypothalamus where the aquaporin 4 receptorhas high rates of expression.
NMO antibody testing is highly sensitive and specific for the diagnosis.