Limb Weakness and Vision Loss in a 30-Year-Old Man

Sumaira Nabi, MBBS; Shahzad Ahmed, MBBS; Muhammad Tariq, MBBS, FRCP

Disclosures

November 10, 2015

NMO is characterized by attacks of unilateral or (less often) bilateral optic neuritis and myelitis that usually occur sequentially rather than simultaneously.[2] Although, as Devic observed, these two conditions can follow in quick succession, in some cases they may be separated by an interval of years or even decades.[2,7] Typically, the history is significant for a painful visual loss with severe paraplegia, sensory loss, and bladder dysfunction. Cervical myelitis can extend into the brainstem, leading to intractable hiccups, nausea and vomiting, vertigo, various bulbar symptoms, and acute neurogenic respiratory failure.[10,11] Other symptoms of spinal cord demyelination that are seen in multiple sclerosis, such as flexor spasms and Lhermitte phenomenon, may also be seen in NMO.

MRI of the spine typically reveals longitudinally extensive transverse myelitis (LETM), with lesions extending over three or more vertebral segments. These necrotizing and cavitating lesions are predominantly located in the cervical and thoracic cord and are hypointense on T1-weighted imaging and hyperintense on T2-weighted imaging and FLAIR sequences. Cord swelling and gadolinium enhancement are seen in acute cord lesions.[12,13] MRI of the brain is typically normal except for optic nerve enhancement by intravenously administered gadolinium during an acute attack of optic neuritis. Nonspecific white matter lesions may be seen in some patients.[14] Brainstem lesions can occur in isolation or as an extension of cervical myelitis. They can be detected in 60% of patients with NMO later in the course of the disease and are usually clinically silent.[15]

Cerebrospinal studies may also aid in the diagnostic process. CSF pleocytosis (>50×106 leukocytes/L) with a neutrophilic predominance is a characteristic of NMO.[16] Oligoclonal bands are usually absent but may be found in 15%-30% of patients with NMO.[17] Identification of NMO immunoglobulin G (IgG) as the pathogenic biomarker has contributed to widening the spectrum of NMO. These antibodies are directed against the aquaporin-4 water channels in the astrocyte foot processes at the blood-brain barrier, pia, subpia, and Virchow-Robin spaces. NMO IgG has a sensitivity of 73% and specificity of 91%.[18]

NMO is defined using the revised diagnostic criteria devised by Wingerchuk and colleagues in 2006,[19] which require the presence of optic neuritis and myelitis plus any two of the following: (1) brain MRI scan not satisfying the McDonald criteria; (2) T2-weighted MRI scan showing contiguous spinal cord lesions spanning three or more vertebral segments; and/or (3) positive serology for NMO IgG (anti-aquaporin-4 antibody). Our patient fulfilled these criteria.

Since the discovery of NMO IgG, various limited forms of NMO have also been recognized based on NMO-IgG seropositivity; these constitute the NMO spectrum disorders.[20] These include the following clinical presentations: idiopathic single or recurrent attacks of LETM, recurrent or simultaneous bilateral optic neuritis, Asian-type (opticospinal) multiple sclerosis, optic neuritis or LETM associated with systemic autoimmune diseases, and optic neuritis or LETM associated with brain lesions typical of NMO.

NMO is now recognized as a discrete demyelinating disorder, with clinical, neuroimaging, and laboratory findings that can distinguish it from multiple sclerosis.[2,20] Multiple sclerosis may involve any white matter tract and has milder attacks. NMO involves the optic nerves and spinal cord only, with more severe attacks. Brain MRI scans are usually normal or nonspecific in NMO, whereas those in multiple sclerosis show periventricular and other white matter lesions. In addition, spinal cord MRI scans reveal longitudinally extensive, central necrotic lesions in NMO, whereas multiple small peripheral lesions are seen in multiple sclerosis. CSF oligoclonal bands are typically absent in NMO, unlike in multiple sclerosis, and NMO may be associated with a coexistent autoimmune disease.[20]

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