from Seminars in Neurology (Semin Neurol 22(2):105-122, 2002.)
10th January 2003
Bruce A.C. Cree, M.D., Ph.D., Douglas S. Goodin, M.D., Stephen L. Hauser, M.D.
Department of Neurology, University of California San Francisco, San Francisco, California
Abstract and Introduction
Whether neuromyelitis optica (NMO), the co-occurrence of myelitis and optic neuritis, is a variant of multiple sclerosis (MS) or a unique disease is controversial. Distinct neuropathological features and a fulminant clinical course argue in favor of NMO as a distinct disease. However, the combination of neurological impairments of myelitis and optic neuritis occurs in patients with several inflammatory disorders, including multiple sclerosis and collagen vascular diseases. NMO is also associated with certain infectious diseases. The fact that the NMO phenotype occurs in a variety of disease states suggests that NMO does not represent a specific clinical entity. To better understand NMO and its associations with recognized diseases, a systematic review of the literature using MEDLINE was conducted. The history of NMO, its nosology, associations with other diseases, and current concepts of its pathogenesis and treatment is reviewed in this article.
Objectives: On completion of this article the reader will be able to recognize the clinical presentation, summarize the state-of-the-art diagnostic workup and differential diagnosis, and outline the contemporary views on management of neuromyelitis optica.
Accreditation: The Indiana University School of Medicine is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians.
Credit: The Indiana University School of Medicine designates this educational activity for a maximum of 1.0 hours in category one credit toward the AMA Physicians Recognition Award. Each physician should claim only those hours of credit that he/she actually spent in the educational activity.
Disclosure: Statements have been obtained regarding the authors' relationships with financial supporters of this activity. There is no apparent conflict of interest related to the context of participation of the authors of this article. Dr. Goodin has (or currently is) participating in industry-sponsored clinical trials in multiple sclerosis with the following pharmaceutical companies: Ares-Serono, Berlex Laboratories, Biogen, Immunex, and Teva-Marion Partners. This article discusses the use of DMTs in multiple sclerosis not limited to labeled use.
The syndrome of neuromyelitis optica (NMO) is defined as the co-occurrence of optic neuritis with myelitis. This combination of neurological impairments occurs in patients with multiple sclerosis (MS), acute disseminated encephalomyelitis (ADEM), systemic lupus erythematosus (SLE), and Sjögren syndrome. It also occurs in association with viral and bacterial infections. However, most often, no underlying cause can be found. The clinical course of NMO is variable. It may occur as a monophasic illness that is either fulminant and fatal or associated with varying degrees of recovery. Polyphasic courses characterized by relapses and remissions also occur. Over the last century much debate has revolved around whether NMO is a distinct disease, at least in a subset of patients, and what its relationship is to MS and other inflammatory disorders. This review focuses on the history of NMO, its nosology, reported associations with other disorders, and current concepts of pathogenesis. Whether or not the NMO phenotype corresponds to a unique biologic process will await the identification of a disease-specific marker and, ultimately, the elucidation of the syndrome's pathogenesis.
The English-language literature was systematically searched using MEDLINE with the keywords neuromyelitis optica or Devic's disease. All articles available through the University of California library system were reviewed. Additional articles referenced in bibliographies from these articles were also reviewed. Some of these references were translated into English for review. Additional selected references from the 19th and early 20th century were obtained. Case reports that revealed further insights into NMO, not identified in case series, were included in the analysis.
In 1870, the first account of an association between myelitis and an optic nerve disorder was reported by T.C. Allbutt. He described a case of myelitis followed by optic nerve changes approximately 3 months later; however, details of the case report are scant and pathology was not presented. Erb (1879) published a case report of a 52-year-old man who developed recurrent optic neuritis followed by transverse myelitis. The patient made a partial recovery from his myelopathy but had sustained impairments in visual acuity. In the same year Steffan described a similar case. Seguin (1880) reviewed Erb's case, a case of Noyes, and a third case of optic neuritis and subacute transverse myelitis that he observed personally. He considered the association to be accidental and not a clinical syndrome. Dreschfeld (1882) described the first case of optic neuritis and myelitis that was autopsied and demonstrated inflammatory changes in the spinal cord and optic nerves. In contrast, examination of the brain was normal. Dreschfeld credited Gowers for recognizing that "the optic neuritis and the myelitis were both the result of a common cause," and this report first suggested that this combination of symptoms is a clinical syndrome.
Several additional cases were also described in the early medical literature.[7-9] Devic's student Gault (1894) reviewed 16 previously reported similar cases and studied another case for his doctoral thesis.[10-12] Gault and Devic proposed that these cases of optic neuritis and myelitis represented a distinct clinical entity: "neuromyélite optique aiguë." Using the clinical criteria proposed by Gault and Devic, additional case reports of NMO gradually accumulated in the literature and were successively reviewed by Goulden (1914, 52 cases), Beck (1927, 71 cases), Stansbury (1949, 200 cases), and Peters (1958, 300 cases). Many cases included in these reviews had pathological changes in the brainstem and cerebrum that in retrospect are consistent with other diagnoses such as ADEM, acute MS (Marburg variant), and relapsing MS. Other cases are probably secondary to infectious (syphilis or measles) or toxic (lead and cadmium poisoning) etiologies. Thus, in all likelihood, the broad clinical definition of NMO used in these studies allowed inclusion of cases with diverse etiologies. As a result, several authors began to question the concept of NMO as a unique disease.[17,18]
Neuromyelitis Optica as a Distinct Disease
In support of the view that NMO can be a unique disease are the striking neuropathological features that were reported in typical cases of NMO. Demyelination of the optic nerves and infiltration of the spinal cord with inflammatory cells were recognized in many early cases.[6,9-12,19] For example, Beck (1927) described rarefaction of the spinal cord and optic nerves, polymorphonuclear infiltrates, extensive demyelination, and destruction of the spinal cord extending continuously through multiple segments. These features were felt to be distinct from the pathology observed in MS. Similarly, Hassin (1937) and Lowenberg et al (1947) described involvement of both gray and white matter of the spinal cord, marked inflammatory infiltrates, and the absence of gliosis, changes that were thought to be distinct from findings in both MS and necrotic myelitis.
Stansbury (1949) reviewed the neuropathology of 20 cases of NMO and proposed that the lesions progressed through a series of stages. The earliest stage is characterized by acute inflammation: lesions show prominent perivascular exudates of polymorphonucleocytes, leukocytes, and plasma cells. The next stage is characterized by evidence of tissue destruction and demyelination in the perivascular foci. In this stage, smaller lesions seem to coalesce into larger lesions, and axis-cylinder destruction is noted. Gray matter structures of the cord may be involved either alone or by extensions from adjacent white matter lesions. Necrotic lesions are frequently observed in the cord, and smaller necrotic foci are sometimes found within the optic nerves. The next stage is characterized by reactive microgliosis. Numerous microglial cells, frequently with lipid-laden phagosomes containing myelin, are typically seen in this stage. The final stage is characterized by astrocytosis and the formation of glial scars. Stansbury noted that glial scarring is less frequent and usually only partial, in contrast to typical MS plaques.
Neuromyelitis Optica as a Subtype of Other Demyelinating Disorders
The fact that many of the pathological findings in NMO are also present in typical cases of MS led many authors to consider NMO as a form of MS. Dreschfeld recognized that "acute disseminated myelitis" (neuromyelitis optica) and "diffuse sclerosis" (multiple sclerosis) were similar. Although some of the reported cases of NMO had a chronic course, the cases that came to autopsy were typically fulminant. As a result, it is possible that the pathological differences observed between NMO and MS reflect the severity of the demyelinating attack and not a distinct pathological process. In the discussion of Lowenberg et al's (1947) observations on NMO and its relationship to MS and necrotic myelitis, Putnam (1947) noted that necrosis of the spinal cord was unlikely to occur in patients with NMO who recovered from an acute attack; thus, lesions in the remitting cases were probably different from lesions in autopsied cases. Furthermore, Putnam and Forster (1942) described 6 of 12 patients with NMO who eventually developed other neurological signs consistent with MS; thus, these authors suggested that NMO was a presentation of MS. This view was shared by Ferraro (1937), who considered all forms of demyelinating disease to be varying presentations with the same primary etiology, a "neuroallergic reaction."
Several cases of NMO in the early literature had diffuse brain involvement. In retrospect, such cases are most likely examples of ADEM. Indeed, Miller and Evans, citing similarities in pathology, suggested that NMO was a form of ADEM. Both NMO and ADEM can produce both gray and white matter involvement, perivascular infiltration, and areas of focal necrosis. However, such an explanation fails to account for cases of NMO that have a relapsing-remitting course.
Several sets of diagnostic criteria for NMO have been proposed (Table
1). However, none has received widespread acceptance. For example, the
criteria of Gault and Devic seem too broad and do not exclude coexistent
myelitis and papillitis from infection, injury, or tumor. Undoubtedly,
this resulted in some confusion in the early literature. By contrast, the
definition used by Shibasaki et al is probably too restrictive, excluding
polyphasic cases or those that evolve over more than 1 month. The criteria
of O'Riordan et al allow for polyphasic and unilateral optic neuritis cases
but are also probably too restrictive in requiring the myelitis to be both
rapid and transverse. The newer criteria of both Mandler et al and Wingerchuk
et al utilized magnetic resonance imaging (MRI) to exclude alternative
diagnoses. However, specific MRI features that distinguish NMO from other
demyelinating disorders are not well described. Nevertheless, refinements
used to define NMO incorporating MRI imaging in the diagnostic algorithm
have led to the identification of a subset of patients who seem different
from typical MS patients in terms of their disease severity, prognosis,
and response to treatment.
|Table 1. Comparison of the Definitions of Neuromyelitis Optica|
|Gault and Devic (Lyon, France)[10-12]
Diagnosis requires all absolute criterion and one major supportive criteria or two minor supportive criteria
NMO is a rare syndrome in Western countries, constituting less than
1% of demyelinating disease.[24,25] Clinical, MRI, and spinal fluid features
from several case series are summarized in Table 2. Men and women were
initially thought to be equally affected, although in more recent case
series women are overrepresented.[15,26-31] The age of onset ranges from
childhood to late adulthood[27,33-36] with the incidence apparently
tapering off after the fifth decade. Cases can present with either
visual loss or myelopathy. Occasionally, optic nerve and spinal cord symptoms
begin simultaneously. Either one or both eyes may be involved, and the
extent of myelitis is variable. In most cases, involvements of the spinal
cord and optic nerves occur within 3 months of each other, although some
authors have included patients with 2 or more years between these occurrences.
Approximately one third of cases are preceded by a prodrome of fever, myalgia,
headache, or sore throat.[29,37] Generally, NMO is sporadic, although there
are a few case reports of familial occurrences.[38-40]
|Table 2. Clinical Features of Neuromyelitis Optica Combined from Recent Case Series[26-29,31]|
|Average age at onset||37|
|Optic neuritis presentation||50 (45%)|
|Transverse myelitis presentation||43 (38%)|
|Combined ON/TM presentation||19 (17%)|
|Autoimmune disease/antibodies||28/104 (27%)|
|Antecedent infection||22/91 (24%)|
|Normal brain (MRI)||48/63 (76%)|
|Abnormal spinal cord (MRI)||55/58 (95%)|
|CSF pleocytosis||63/85 (74%)|
|>50 cells/mm3||27/84 (32%)|
|CSF polymorphonucleocytes||34/67 (51%)|
|CSF oligoclonal bands||23/77 (30%)|
CSF, cerebrospinal fluid; MRI, magnetic resonance imaging; ON/TM, optic neuritis/transverse myelitis.
NMO is often fulminant and acute, as described in the early literature. Some patients have a monophasic illness, especially in the pediatric population. Others have polyphasic illness characterized by relapses and remissions with variable degrees of recovery between episodes (Table 2). The proportion of patients in each of these two groups varies depending on the criteria used to define NMO (Table 1). One series found that approximately one third of patients with relapsing NMO die from respiratory failure as a consequence of diaphragmatic paralysis from cervical cord lesions. In this series, the most important prognostic factor was whether the disease had a monophasic or polyphasic course. The 5-year survival rate for patients with a monophasic course, typified by closely clustered occurrence of bilateral optic neuritis with myelitis (occurring within 1 month), was 90%. In contrast, the 5-year survival rate for patients with recurrent disease was 68%.
In the pediatric population, NMO is frequently preceded by infection (72%). Pediatric cases typically have a monophasic course and many have complete neurological recovery.[32,41] Because of pediatric NMO's frequent association with preceding infection, monophasic course, and generally good outcome, some authors consider pediatric NMO to be a variant of ADEM.[32,42]
The differential diagnosis for cases of NMO is concise. Cases have been
associated with collagen vascular disease and infectious, toxic, and idiopathic
The association of NMO with systemic and infectious disease is discussed
later. A list of possible associated etiologies and potential diagnostic
studies is presented in Table 3.
|Table 3. Approach to the Neuromyelitis Optica Syndrome|
|Collagen vascular diseases and autoantibody syndromes|
|Systemic lupus erythematosus|
|Mixed connective tissue disease|
|Viral and mycobacterial infections|
|Idiopathic central nervous system demyelinating diseases|
|Asian-type multiple sclerosis|
|Western-type multiple sclerosis|
|Acute disseminated encephalomyelitis|
|Complete history, physical, and neurological examination|
|Basic laboratory studies|
|Complete blood count, serum chemistries, urinalysis with microscopic examination, chest X-ray with posteroanterior and lateral views, HIV testing, and PPD placement with controls for anergy|
|Spine, brain, and optic nerves with and without gadolinium contrast administration|
|Cell counts, total protein, glucose, IgG index, IgG synthetic rate, oligoclonal bands, VDRL, polymerase chain reaction for herpes zoster virus and Epstein-Barr virus, bacterial and mycobacterial stains and cultures|
|Collagen vascular disease studies|
|ESR, ANA, ds-DNA, ENA, p-ANCA, anticardiolipin antibodies, rheumatoid factor, anti-SSA and anti-SSB antibodies|
|For a patient with serological markers for Sjögren syndrome or a history of xerostomia and xerophthalmia, consider a Schirmer test (lacrimation), salivary gland scintigraphy, and salivary gland/lacrimal gland biopsies|
ANA, antinuclear antibody; ds-DNA, double-stranded DNA; ENA, extractable nuclear antigen; ESR, erythrocyte sedimentation rate; HIV, human immunodeficiency virus; IgG, immunoglobulin G; p-ANCA, perinuclear antineutrophil cytoplasmic antibody; PPD, purified protein derivative; SSA, Sjögren syndrome antigen A; SSB, Sjögren syndrome antigen B; VDRL, Venereal Disease Research Laboratory.
It is not currently possible to predict whether a patient presenting
with optic neuritis or myelitis will develop NMO. The co-occurrence of
bilateral optic neuritis should raise concern about the development of
subsequent myelitis. However, because of the rarity of NMO in Western countries,
bilateral optic neuritis is still more commonly associated with the subsequent
development of MS than NMO in these environments. Although a schema
for the comprehensive evaluation of optic neuritis is beyond the scope
of this review, its differential diagnosis is presented in Table 4.
|Table 4. Approach to Optic Neuritis|
|Collagen vascular diseases|
|Systemic lupus erythematosus|
|Autoimmune optic neuropathy|
|Herpes zoster virus|
|Human immunodeficiency virus (HIV)|
|Hepatitis A virus|
|Mycobacterium tuberculosis (tuberculosis)|
|Borrelia burgdorferi (Lyme disease)|
|Treponema pallidum (syphilis)|
|Bartonella henselae (cat-scratch disease)|
|Toxoplasma gondii (toxoplasmosis)|
|Paraneoplastic optic neuritis|
|Idiopathic demyelinating diseases|
|Idiopathic optic neuritis|
|Acute disseminated encephalomyelitis|
|Optic neuritis mimics|
|Infiltrating neoplasms (e.g., lymphoma, leukemia, myeloma, carcinomatous meningitis)|
|Optic nerve glioma|
|Optic nerve glioblastoma|
|Optic sheath meningioma|
|Langerhans cell disorders|
|Cancer-associated retinopathy (CAR)|
|Cancer-associated cone dysfunction (CACD)|
|Melanoma-associated retinopathy (MAR)|
|Diffuse uveal melanocytic proliferation (DUMP)|
|Paraneoplastic ganglion cell neuronopathy (PCGN)|
|Nonarteritic anterior ischemic optic neuropathy|
|Giant cell arteritis|
|Microangiopathy of the brain, retina, and inner ear (Susac's syndrome)|
|Acute posterior multifocal placoid pigment epitheliopathy|
|Eale's disease (noninflammatory occlusive disease of the retinal vasculature)|
|Cogan's syndrome (interstitial keratitis, vestibular dysfunction, and deafness)|
|Central retinal vein occlusion|
|Aneurysms and arteriovenous malformations|
|Systemic hypercoaguable states, including anticardiolipin syndrome|
|Nutritional and toxic|
|Vitamin B12 deficiency|
|Toxins (e.g., ethyl alcohol, ethambutol, methanol, amiodarone, clioquinol, chemotherapeutic agents)|
|Radiation-induced optic neuropathy|
|Genetic mitochondrial disease|
|Leber's hereditary optic neuropathy|
|MELAS (mitochondrial encephalopathy with lactic acidosis and strokes)|
|NARP (neuropathy, ataxia, and retinitis pigmentosa syndrome)|
|Central serous chorioretinopathy|
|Optic disc drusen|
|Big blind spot syndromes (acute zonal occult outer retinopathy, acute macular neuroretinopathy, multiple evanescent white dot syndrome, acute idiopathic blind spot enlargement syndrome)|
The development of progressive myelopathy in the absence of antecedent
neurologic symptoms and without signs indicating dissemination beyond the
spinal cord is a diagnostic challenge. In such patients, once compressive
etiologies have been excluded, MS is the most common cause of this syndrome
in the Western world. Clinically useful features that suggest an MS origin
for a progressive myelopathy include painless presentation; no systemic
symptoms; asymmetric involvement of the cord; no family history of myelopathy;
MRI evidence of multifocal cord or brain white matter involvement; abnormal
brainstem or visual evoked responses; and a cerebrospinal fluid (CSF) profile
with variable mononuclear cell pleocytosis, no polymorphonuclear leukocytes
or eosinophils, normal glucose and total protein, increased immunoglobulin
G (IgG) synthesis, and oligoclonal bands. Features of myelitis that may
suggest impending optic nerve involvement are the presence of polymorphonucleocytes
or eosinophils and the absence of oligoclonal bands in the CSF, a normal
brain MRI scan, and abnormal visual evoked potentials. An approach to the
differential diagnosis and diagnostic work-up for acute myelitis presentations
is outlined in Table 5.
|Collagen vascular diseases and autoantibody syndromes|
|Systemic lupus erythematosus|
|Mixed connective tissue disease|
|Primary angiitis of the central nervous system|
|Hashimoto's encephalopathy (myelopathy)|
|Herpes simplex 1 and 2|
|HTLV-I, HTLV-II with HIV coinfection|
|Hepatitis A, B, C|
|Group B arboviruses (West Nile and dengue)|
|Lymphocytic choriomeningitis virus|
|Bacterial and mycobacterial infections|
|Borrelia burgdorferi (Lyme disease)|
|Brucella melitensis (brucellosis)|
|Treponema pallidum (syphilis)|
|Bartonella henselae (cat-scratch disease)|
|Clostridium tetani (tetanus)|
|Mycobacterium tuberculosis (tuberculosis)|
|Bacterial meningitis, intraparenchymal abscess, and epidural abscess|
|Schistosoma haematobium, Schistosoma mansonii, Schistosoma japonicum Toxocara spp.|
|Toxic exposure and nutritional deficiency|
|Antitubercular medication exposure|
|Subacute combined degeneration (vitamin B12 deficiency)|
|Demyelinating and dysmyelinating diseases|
|Acute disseminated encephalomyelitis|
|Lymphoma, leukemia, and other infiltrating tumors|
|Paraneoplastic: Hodgkin's lymphoma|
|Spinal dural arteriovenous malformation|
|Complete history (including travel and animal contacts), physical, and neurological examination|
|Basic laboratory studies|
|Complete blood count, serum chemistries, vitamin B12, urinalysis with microscopic examination, chest X-ray with posteroanterior and lateral views, HIV testing, and PPD placement with controls for anergy|
|Spinal cord with and without gadolinium contrast administration; brain with and without gadolinium contrast administration and with sagittal T2- or proton density-weighted images|
|Visual evoked potentials and nerve conduction studies|
|Collagen vascular disease and autoantibody studies|
|ESR, ANA, ds-DNA, ENA, RF, anti-SSA, anti-SSB, anticardiolipin antibodies, and p-ANCA; thyroid function tests, antimicrosomal antibodies, and antithyroglubulin antibodies for Hashimoto's encephalopathy (myelopathy)|
|For a patient with serological markers for Sjögren syndrome or a history of xerostomia and xerophthalmia, consider a Schirmer|
|test (lacrimation), salivary gland scintigraphy, and salivary/lacrimal gland biopsies|
|Cell counts, protein, glucose, IgG index, IgG synthetic rate, oligoclonal bands, angiotensin-converting enzyme|
|CSF infectious etiology studies|
|PCR for varicella-zoster, Epstein-Barr, herpes simplex type I and II, and cytomegalovirus viruses; antibody studies for human T-cell lymphotrophic virus type I, Borrelia burgdorferi, Mycoplasma pneumoniae, and Chlamydia pneumoniae; viral cultures for enteroviruses; cultures and stains for aerobic and anaerobic bacteria, fungi, Mycobacterium tuberculosis and Brucella melitensis; and VDRL|
|Serum infectious etiology studies|
|IgG and IgM enterovirus antibody titers, IgM mumps, measles, and rubella antibodies, group B arbovirus antibodies (West Nile and dengue), Brucella melitensis antibodies, Chlamydia psittaci antibodies, Bartonella henselae antibodies, schistosomal antibodies; cultures for Brucella melitensis, hepatitis A, B, and C studies, and RPR|
|Additional studies for infection|
|Nasal-pharyngeal and anal swabs/cultures for enteroviruses; stool O&P for Schistosoma ova; wound cultures for Clostridium tetani (if applicable)|
|Serum angiotensin-converting enzyme (ACE), serum calcium, and 24-hour urine calcium; for patients with hilar adenopathy or elevated ACE, consider CT of chest, total body gallium scan, and lymph node biopsy to search for systemic sarcoidosis|
|Serum and 24-hour urine for very long chain fatty acids for adrenomyeloneuropathy|
|CT myelogram and spinal angiogram for spinal dural arteriovenous malformation|
ANA, antinuclear antibody; CT, computed tomography; ds-DNA, double-stranded DNA; ENA, extractable nuclear antigen; ESR, erythrocyte sedimentation rate; HIV, human immunodeficiency virus; HTLV, human T-cell lymphotropic virus; IgG, immunoglobulin G; O&P, ova and parasites; p-ANCA, perinuclear antineutrophil cytoplasmic antibody; PPD, purified protein derivative; RF, rheumatoid factor; SSA, Sjögren's syndrome antigen A; SSB, Sjögren syndrome antigen B; VDRL, Venereal Disease Research Laboratory.
Physical Examination Findings
Ophthalmoscopic examination may be normal or find signs of optic neuritis with blurring of the discs. Some patients have mild papilledema, although hemorrhages and exudates are rare. Optic atrophy with disc pallor may be seen in chronic cases. Visual field testing typically reveals a central scotoma, although other visual field changes such as color blindness, bitemporal hemianopsia, paracentral scotoma, and altitudinal deficits are reported. The pupils are dilated in response to the visual loss but are otherwise normal. Extraocular movement abnormalities, Horner's syndrome, and nystagmus were reported by some authors, although in retrospect these cases were probably misclassified.
The spinal cord symptoms in NMO are not different from those of other causes of myelitis. Some authors maintain that the myelitis should be transverse and complete, although not all cases adhere to this requirement. Lhermitte's symptom is frequent and patients may suffer from painful tonic spasms.[47,48] Cerebral and brainstem findings should not be present; if they are present, a search for alternative etiologies is warranted.
CSF. The CSF is often abnormal with mildly elevated protein and the presence of pleocytosis including polymorphonucleocytes. Cell counts vary broadly and are reported to be as high as 3000 cells/mm3. In recent case series cell counts over 50 have been reported in as many as one third of patients, although such elevated cell counts should raise suspicion of alternative diagnoses. The opening pressure is usually normal but can be elevated. Oligoclonal bands can be present but are reported to be seen less often than in typical cases of MS.[26,27,29]
Imaging. The spinal cord MRI is typically abnormal with areas of increased signal intensity spanning several sections of the spinal cord on T2-weighted images and with gadolinium enhancement (Fig. 1).[28,29,51,52] Swelling of the cord may occur and can sometimes be mistaken for a tumor.[26,53] The optic nerves can also be enhanced with gadolinium on TI-weighted images. By contrast, the brain MRI is often normal or may show nonspecific changes. One study directly compared brain MRI scans from typical MS patients with those in NMO and found lesions in T2-weighted images in one of seven NMO patients in contrast to multiple lesions observed in all patients with MS. Another study noted that with serial scans intraparenchymal white matter lesions can evolve over time in patients with NMO. A brain MRI study without evidence of demyelination at the time of presentation is considered by some to be important in establishing a diagnosis of NMO.
Figure 1. (click image to zoom) Cervical spinal cord MRI in the sagittal plane of a 28-year-old woman with polyphasic neuromyelitis optica. (A) T1-weighted image showing thickening of the cord from C7 to T2 with patchy areas of subtle intraparenchymal hyperintensity. (B) T1-weighted image, post gadolinium contrast administration, showing several enhancing lesions from C7 to T2. (C) T2-weighted image showing a contingous area of increased signal intensity spanning from C6 to T3.
Asian-Type (Opticospinal) Multiple Sclerosis and Neuromyelitis Optica
Neuromyelitis Optica and Multiple Sclerosis In Japan
The prevalence of MS in Japan is estimated to be 1.6 to 1.8 per 100,000, substantially lower than in Western countries. However, the proportion of patients with NMO in this population is reported to be higher than in Western populations. Okinaka et al collected 270 cases of demyelinating disease diagnosed in Japan between the years 1890 and 1955. Clinical involvement was restricted to the spinal cord and optic nerves in 145 of these cases. The very high numbers with presumed NMO in this series suggested that NMO is more prevalent than typical MS in Japan; however, sampling bias makes this interpretation uncertain. Kuroiwa and colleagues[57-59] reviewed cases of demyelinating disease at Kyushu Hospital from 1958 to 1973. They found 63 cases of MS; 59 met Schumacher criteria for MS, and 4 were autopsy proved. Spinal cord and optic nerve presentations were observed in 51% of these cases. In addition, six cases of acute monophasic NMO were identified, corresponding to 6% of all cases of demyelinating disease. Although this estimate is considerably lower than the prior estimates, it is still much higher than in Western case series. Kuroiwa and colleagues collected 1084 patients with MS from across Japan in 1972 to 1973. Eighty-two (7.6%) met their criteria for NMO (Table 1), again demonstrating a high proportion of NMO in Japan. When the cases from this survey of probable MS (Schumacher criteria) and classic NMO are combined, 82% had optic nerve involvement and 82% had spinal cord involvement. These data indicate that demyelinating disease in the Japanese has a predilection for involvement of the optic nerves and spinal cord.
Pathology of Japanese Multiple Sclerosis
In an attempt to correlate pathologic changes with the clinical presentations of cases of demyelinating disease in Japan, Shibasaki and Kuroiwa analyzed 54 autopsied cases. Of 13 cases of NMO, 4 had lesions restricted to the optic nerves and spinal cord; additional lesions were present in the brainstem in 8 patients and in the cerebrum in 4 patients. The majority of cases (9 of 13) had lesions that were not confined to the spinal cord and optic nerves, underscoring the heterogeneity of clinically defined NMO. Moreover, the pathological changes in some cases were consistent with both MS and NMO, demonstrating that overlap occurs between these conditions. These observations led Kuroiwa and colleagues to conclude that NMO was a type of MS and that the majority of patients in Japan suffered from "opticospinal" MS. Opticospinal MS was considered to be a transitional form of MS combining features of the more aggressive acute NMO and typical Western-type MS. In Caucasians, a clinical predilection for optic neuritis and/ or spinal cord involvement was found to aggregate in some multicase MS families, further supporting a biological basis for an opticospinal phenotype.
Comparison of Multiple Sclerosis in Asian Populations
In a survey of MS in Asian countries, Kuroiwa and colleagues found several patterns that distinguish MS in Asia from MS in Western countries. Visual impairment occurred in 70% of patients in this series in comparison with 34% from a U.S. Army series. In addition to the frequent occurrence of visual impairment, which was often bilateral and severe, presentations of NMO were not rare. The authors proposed that demyelinating disease in Western and Asian countries shared a common pathogenesis, with typical Western MS and classic NMO being at opposite ends of a continuum. In a comparison of patients from Japan and England, Shibasaki and colleagues found that visual loss at the onset of illness and severe visual deficits were more frequent in Japanese patients. Frequent and severe involvement of the spinal cord and brainstem was also more common in the Japanese than in the English. A low incidence of MS and relatively higher proportion of NMO were also reported in Malaysia and India.[66-71]
Observed clinical differences between Eastern and Western MS led to the hypothesis that the clinical phenotype of demyelinating disease in Asian-type MS may be due to immunogenetic variation. Kira and colleagues studied the HLA locus in a series of Japanese patients with MS. They found that, unlike the findings in Western MS, the DR2-associated DRB1*1501 and DRB5*0101 alleles were not associated with NMO (0%). Additional support for an immunogenetic contribution to the phenotype of Asian MS came from further studies of the human leukocyte antigen (HLA) locus.[74-76] DPA1*0202 and DPB1*0501 alleles were associated with the NMO phenotype in Japanese patients but not with healthy control subjects or Japanese patients with typical MS. The HLA alleles with the strongest association with Western-type MS in Japanese patients were found to be DRB1*1501 and DRP1*0301. These findings are consistent with an association of the extended DRB1*1501, DQB1*0602 haplotype with the disseminated form of MS. This finding has been consistent in many, but not all, studies. Linkage disequilibrium between the DR and DP loci is considerably less tight than between the DR and DQ loci. Whether the DPA1*0202 and DPB1*0501 alleles will be found to correlate with NMO in other Asian or Western patients remains to be seen.
The clinical course of MS in Japan may be changing. Fewer patients present with Asian-type (opticospinal) MS and relatively greater numbers present with Western-type MS. Nakashima and colleagues found that 60% of cases collected from the 1970s had opticospinal MS. In comparison, only 5% of cases collected form the 1990s had the Asian MS phenotype. It is possible that increased awareness of MS in Japan has led to the identification of cases of Western-type MS that would not have been recognized previously because of the assumption of the rarity of the disease in Japan. Nevertheless, this striking observation also argues for an environmental influence on the clinical phenotype of MS because the genetic background in Japan has not changed significantly during the 30 years spanned by this study. The increased travel of Japanese to Western countries and vice versa hypothetically may have led to the introduction into Japan of infectious or toxic agents or of lifestyle, including dietary, adaptations that may influence the phenotype of central nervous system (CNS) demyelinating disease.
Neuromyelitis Optica in Tropical Countries
Although genetic factors such as the HLA locus are likely to influence the clinical manifestations of demyelinating disease, environmental factors may also play a role. NMO occurs in individuals with diverse genetic backgrounds who reside in tropical environments, raising the possibility that this phenotype may be promoted by an environmental trigger or triggers prevalent in these areas of the world. Further studies are needed to elucidate the interaction between genetic and environmental factors that predispose persons of certain racial groups to NMO.
Osuntokun reviewed hospital records in Nigeria from 1957 to 1969 to survey all cases of neurological disease. Interestingly, he found 2 cases of MS but identified 95 cases of NMO, estimating a prevalence of 43 per 100,000 of hospital cases. Autopsy confirmation was not available for this case series. Nevertheless, these findings are consistent with the observation that MS is rare in the tropics. However, if one considers NMO to be a form of MS, then the prevalence of 43 per 100,000 hospital cases is comparable to that in similar series in Western hospitals. That NMO was present in 98% of cases of identified demyelinating disease in Nigeria is striking and warrants further investigation.
The polyphasic NMO phenotype was also observed in seven of eight black South African patients with CNS demyelinating disease. Oligoclonal bands were not found in any of these patients. MRI imaging of the spinal cord revealed lesions that spanned several segments of the spinal cord, and MRI imaging of the brain showed disseminated lesions in the cerebral white matter consistent with MS. This pattern is reminiscent of the opticospinal form of MS observed in Japanese patients. The almost exclusive occurrence of the NMO phenotype in native African blacks with MS-like syndromes is strikingly different from the low prevalence of this phenotype in Caucasian patients. This suggests that, at least in this population, NMO may represent a distinct disease.
Cabre and colleagues surveyed French African-Caribbeans in Martinique from 1997 to 1999 and identified 62 cases with definite or probable MS by Poser criteria and 17 cases of NMO by the Wingerchuk et al criteria (17.3% of CNS demyelinating disease). In this series, NMO was found to affect women exclusively and a trend for a lower frequency of oligoclonal bands was observed in the NMO group.
One study of 67 consecutive patients diagnosed with MS in São Paulo, Brazil reported that a high percentage of patients had NMO. Thirty percent of patients had predominantly optic nerve and spinal cord involvement, and 12% had simultaneous bilateral optic neuritis and transverse myelitis (Shibasaki et al's definition of NMO, Table 1). Neither MRI nor autopsy data are available for these patients. The authors compared the high percentage of NMO observed in their series with the Japanese MS literature and concluded that factors other than race give rise to the phenotypic expression of demyelinating disease. This study is best interpreted with caution because the spectrum of demyelinating disease in Brazil is unknown and many levels of bias can occur in case series from a single hospital.
Neuromyelitis Optica in Indigenous Americans
One study of MS in Manitoba, Canada in Algonkian and Athapaskan indigenous people identified seven cases of MS. The disease course in these patients was more aggressive than in typical MS; five of seven patients had the NMO phenotype, although MRI showed scattered lesions throughout the brain. None of these patients had the HLA DRB1*1501 allele that is associated with Western-type MS. The pattern of CNS demyelinating disease in these patients is reminiscent of that in Japanese MS patients with the NMO phenotype. In the one case in which autopsy data were available, necrosis and inflammatory infiltrates were present in the spinal cord. One optic nerve showed mild demyelination and the other severe axonal loss. Demyelinating plaques in the cerebral hemispheres were also present. These findings are similar to the autopsy results for several Japanese patients who presented with the NMO phenotype but were found to have pathological findings of both NMO and MS.
Neuromyelitis Optica with Endocrinopathies
Vernant and colleagues described a series of eight women from Martinique and Guadeloupe who suffered from NMO and endocrinopathies. Seven of the eight patients had secondary amenorrhea that coincided with exacerbations of NMO. One postmenopausal patient and two others had galactorrhea with hyperprolactinemia. Four patients had hypothyroidism, and one patient had diabetes insipidus. The authors suggested that three patients who were hyperphagic and obese suffered from hypothalamic dysfunction. In one patient, a thyrotropin-releasing hormone stimulation test indicated hypothalamic dysfunction as a cause of hyperprolactinemia. In three patients, gadolinium enhancement of the hypothalamic-hypophyseal region was present on brain MRI. All patients suffered from recurrent optic neuritis and myelitis that was resistant to various immunosuppressive therapies and ultimately led to blindness and paraplegia. Oligoclonal bands were found in only one patient. The authors suggested that this series constituted a distinct clinical entity because endocrinopathies were not previously associated with NMO.
Hyperprolactinemia was found in a subset of Japanese patients with MS. Nine of 48 Japanese women with MS had elevated prolactin levels, and 7 of these women had Asian-type MS. Amenorrhea and galactorrhea were present in two women with Asian-type MS. Elevated prolactin levels were not found in Japanese men from the same series. Several patients developed symptoms referable to areas of the CNS other than the optic nerves and spinal cord. The authors suggested that optic nerve inflammation can spread to damage the tuberoinfundibular dopaminergic neurons and subsequently disinhibit prolactin secretion. In theory, prolactinemia may enhance humoral and proinflammatory TH1 cellular responses and thereby augment disease activity. However, prolactin is an acute phase reactant, and circulating levels of this hormone increase in a nonspecific manner in many inflammatory conditions.
Neuromyelitis Optica and Systemic Diseases
NMO has been associated with several systemic diseases including collagen vascular diseases, autoantibody syndromes, infections, and toxic exposures (Table 3). In addition to a complete history and physical examination to look for evidence of systemic disease, specific laboratory testing for many of these conditions should be considered in the evaluation of patients presenting with NMO.
Neuromyelitis Optica in Collagen Vascular Disease
Systemic Lupus Erythematosus. Several case reports associate NMO with SLE. The first published report was that of a 21-year-old woman with a 4-year history of paraparesis and incontinence who developed right-sided retrobulbar optic neuritis. A diagnosis of SLE was made during a prolonged hospital admission. The patient eventually succumbed to bronchopneumonia. Autopsy showed demyelination, inflammatory infiltration, and necrosis of the spinal cord and right optic nerve. No brain lesions were identified, and a diagnosis of NMO was established. The authors estimated that the chances of a patient having both SLE and NMO were 1 in 5,000,000 and considered that chance association in their patient was unlikely. They reviewed the literature on myelopathy and SLE and questioned whether a common pathogenetic mechanism was present in their case. A nonfatal case of NMO complicated the pregnancy of a 27-year-old woman with SLE. In the fourth month of pregnancy she developed transverse myelitis and optic neuritis. MRI studies of the brain and spinal cord were normal. CSF showed an elevated IgG index. The patient was treated with glucocorticoids and plasma exchange, made a complete recovery, and was able to give birth to her child. Transverse myelitis recurred postpartum and again 3 years later. This case is noteworthy because the use of glucocorticoids and cyclophosphamide was associated with complete remission. Currently, a total of 25 similar cases are reported in the literature. A pathophysiological link between SLE and NMO has not yet been established, although some authors have suggested a role for anticardiolipin antibodies and the lupus anticoagulant.[26,31,88-94]
Sjögren Syndrome. NMO was associated with a case of Sjögren syndrome in a 51-year-old woman who presented with subacute transverse myelopathy. The diagnosis was established on the basis of diminished lacrimation and salivation, abnormal antibody studies, and sialography. She was treated with oral glucocorticoids and recovered. However, 7 years later she presented with a sensory level at T6 and acute left optic neuritis that progressed to total blindness. CSF was normal and brain MRI showed swelling of the left intraorbital optic nerve but an otherwise normal brain. She was again treated with glucocorticoids and gradually recovered her vision. This case demonstrates that the combination of transverse myelitis and optic neuritis can be associated with other autoimmune diseases. The authors observed that the anti-Ro (SSA [Sjögren syndrome antigen A]) antibody was present in 7 of 11 patients with optic neuropathy associated with Sjögren syndrome and speculated on a role for this antibody in the pathogenesis of CNS manifestations of Sjögren syndrome, citing cross-reactivity between Ro and HuD, the antigen associated with paraneoplastic encephalomyelitis and sensory neuronopathy.[96,97] Sjögren syndrome was associated with four cases of NMO in the Mayo Clinic series, although details were not provided.
Interestingly, 4 of 13 patients (31%) in the CHRU de Lille series had Sjögren syndrome; although, in three of these cases the diagnosis of Sjögren syndrome was not made until several years after the onset of neurological symptoms. All patients in this series underwent complete screening for Sjögren syndrome including history of xerostomia and xerophthalmia, a Schirmer test, minor salivary gland biopsy, and salivary gland scintigraphy as per the revised European criteria for Sjögren syndrome. The association of NMO with Sjögren syndrome in this series suggests that underlying systemic collagen vascular disease may be underdiagnosed in earlier series that did not include a comprehensive evaluation for Sjögren syndrome.
P-ANCA. NMO was also described in a patient with perinuclear antineutrophil cytoplasmic antibodies (p-ANCA), antinuclear antibody (ANA), SSA, and SSB (Sjögren syndrome antigen B) antibodies. A 52-year-old man presented with transverse myelitis and then, over a 6-month period, developed optic neuritis affecting first the right and then the left eye. Brain MRI was normal but spinal cord MRI showed a contrast-enhancing lesion. He was treated with glucocorticoids but eventually developed permanent bilateral blindness and myelopathy. Sjögren syndrome was excluded despite the presence of anti-SSA and SSB antibodies. The role of p-ANCA antibodies in the pathogenesis of what was considered to be a vasculitic process is uncertain. p-ANCA antibodies were also found in a proportion of Japanese patients with opticospinal type MS.
Anticardiolipin Antibodies. Karussis and colleagues followed a group of 20 MS patients who also had high anticardiolipin (ACL) antibody titers. Patients in this series did not suffer from the ACL syndrome (thrombosis and recurrent abortion), but many experienced a progressive myelopathy and one patient had NMO. Interestingly, ACL titers were also observed in a group of Japanese patients with opticospinal MS; these patients also had high lesion loads on brain MRI. Whether ACL has a role in the pathogenesis of myelitis, NMO, or MS remains to be established.
Mixed Connective Tissue Disease. Neurological manifestations of mixed connective tissue disease (MCTD) are rare, although several case reports associate transverse myelitis with MCTD.[103-105] One report described a 19-year-old woman with MCTD who experienced recurrent bouts of either unilateral optic neuropathy or transverse myelopathy over several years. The patient was treated successfully with plasmapheresis and immunosuppressive medications.
Neuromyelitis Optica in Infectious Disease
Viral. In several series NMO frequently followed an infectious prodrome characterized by headache, myalgia, and upper respiratory symptoms. In a few cases, a known infectious agent was identified. NMO was observed in a 29-year-old man approximately 3 weeks after acute infectious mononucleosis. His CSF was inflammatory; he was treated with glucocorticoid and made a complete recovery. Varicella-zoster infections are associated with acute myelitis, and several case reports associated acute varicella infection with NMO.[108-111] Recovery in these cases was variable despite treatment with acyclovir and corticosteroids. Another report described a 41-year-old woman who presented with left optic neuritis and transverse myelitis in the setting of untreated human immunodeficiency virus (HIV) infection. She underwent a comprehensive work-up for opportunistic infections and granulomatous disease that was not diagnostic. A brain MRI was normal and the CSF was inflammatory but without oligoclonal bands. Her symptoms resolved with antiretroviral medications and glucocorticoid treatment. Given the extraordinary range of neurological complications associated with primary HIV infection, it is plausible that NMO was a consequence of HIV infection. In all of these cases of NMO associated with viral infections the symptoms of optic neuritis and myelitis were separated by a few days to weeks. Thus, when the symptoms of optic neuritis and myelitis co-occur within days to a few weeks, a comprehensive search for possible infectious etiologies is probably warranted.
Tuberculosis. NMO was observed in patients with tuberculosis.[113,114] In these cases, visual loss and myelitis were not thought to be due to direct CNS infection with tuberculosis or antitubercular drugs. In one series, 6 of 10 cases of NMO identified at a South African hospital suffered from pulmonary tuberculosis. The authors interpreted this relationship to be causal, suggesting that an antimycobacterial immune response was involved in the pathogenesis of NMO. However, given that tuberculosis is endemic in this hospital's community, the association may be due to chance.
Subacute Myelo-Optico-Neuropathy. That NMO could have a toxic etiology was suggested by observations of a syndrome that occurred in Japan during the 1960s and consisted of abdominal symptoms followed by transverse myelopathy, optic neuropathy, and peripheral neuropathy. Pathologically, demyelination and axonal injury of the spinal cord, optic nerves, and peripheral nerves was observed. A case-control analysis found a strong association between exposure to clioquinol, an intestinal antiseptic, and the development of subacute myelo-optico-neuropathy (SMON). Subsequent experiments demonstrated that clioquinol can cause myelo-optic neuropathy in dogs.[118,119] Antitubercular treatment was also associated with SMON. From a clinical perspective, SMON may superficially resemble NMO, and in all cases a history of possible toxic exposure should be sought. The presence of peripheral neuropathy clearly distinguishes cases of SMON from those of typical NMO. However, some overlap may occur, as evidenced by one report of typical NMO with evidence of segmental demyelinating peripheral neuropathy demonstrated by teased fiber preparation of the sural nerve.
In experimental autoimmune encephalomyelitis (EAE), various myelin antigens are used to induce autoimmune reactions that serve as models for CNS demyelinating disease. A quantitatively minor myelin protein termed myelin oligodendrocyte glycoprotein (MOG) is highly encephalitogenic in many species and can induce a relapsing or progressive disease with prominent CNS demyelination closely resembling human MS.[122,123] Storch and colleagues[124,125] found that 40% of rats with MOG-induced EAE accumulated selective demyelination of the optic nerves and spinal cord. This may serve as an animal model for NMO. An important distinction of this type of MOG-induced EAE from other antigen-induced forms of acute EAE is the requirement for anti-MOG antibodies for induction of the full demyelinating phenotype to be present. Thus, both T- and B-cell responses play important roles in induction of this MS-like lesion.
A small study found that anti-MOG antibodies were present in four patients with NMO but not in patients with isolated myelitis or optic neuritis, suggesting that autoimmunity against MOG may be a biological marker for NMO in some patients. However, anti-MOG antibodies were also found in some patients with MS and in some control individuals and thus are unlikely to be specific for NMO.[127,128] Further evidence is needed to determine whether anti-MOG antibodies have a role in the pathogenesis of either MS or NMO and, if so, whether some subsets of MOG autoantibodies are pathogenic.
Several autopsied cases of NMO revealed the presence of abnormal vasculature in the spinal cord.[129,130] These changes were compared with the observations of Marie, Foix, and Alajouanine in their description of subacute necrotic myelitis. Many cases of the Marie-Foix-Alajouanine syndrome are thought to be due to necrosis of a dural arteriovenous malformation. The presence of similar vascular abnormalities in some cases of NMO raises the question of an underlying vascular anomaly in some cases. However, it is difficult to rationalize how a spinal dural arteriovenous malformation could produce optic neuritis. Alternatively, the vascular changes observed in some cases of NMO and Marie-Foix-Alajouanine syndrome may be secondary to a primary inflammatory process.
That the spinal cord vasculature may be a target for autoimmune inflammation in NMO is supported by a recent autopsy series, in which NMO lesions were compared to MS, ADEM, and spinal cord infarction lesions. In this study, 100% of actively demyelinating NMO lesions were associated with vessel hyalinization, a finding not present in the MS, ADEM, or infarcted lesions. Furthermore, immunoglobulin, activated complement (C9 neo antigen) and macrophages immunoreactive for myelin proteins, including MOG, co-localized to the perivascular region. These findings suggest that spinal cord blood vessels are targeted for autoimmune attack and that a humoral response with complement activation has a role in tissue destruction. These results are consistent with the observations made by Stansbury who proposed that perivascular inflammation was the initial stage in the pathogenesis of NMO lesions.
Unfortunately, there are no proven effective therapies for NMO. Glucocorticoids are typically used to treat cases acutely and may be beneficial.[29,31,134] Some patients appear to become glucocorticoid dependent and experience relapses when the dosage of prednisone is lowered. Plasma exchange may be tried in patients who do not respond to glucocorticoids. In an uncontrolled case series, 6 of 10 patients with NMO treated with plasma exchange showed moderate or marked improvement. Interferons and sometimes immunosuppressant drugs are used with the hope that further relapses will be prevented, but prospective data in support of their efficacy are lacking.[27,29] In one uncontrolled series seven patients with NMO were treated with long-term prednisone and azathioprine and were observed to improve after 6 months of therapy. Because patients with NMO can improve spontaneously, it is not possible to determine from this uncontrolled series whether this regimen was of any benefit. One case report described a possible benefit of lymphocytaplasmapheresis in a 26-year-old pregnant patient with NMO. Based on recent experimental and pathological evidence, it seems likely that immunoglobulins and complement deposition play a role in the pathogenesis of NMO. Consequently, therapies directed toward inhibiting complement (such as soluble Cr-1), depletion of B-cells (anti-CD20), or plasma exchange should be investigated in randomized, controlled trials.
Since the time when the association of myelitis and optic neuritis was first noted, much debate has focused on whether this observed pattern of illness occurs by chance or represents a distinct clinical entity. In fact, it is now clear that NMO represents a syndrome that can have diverse underlying pathoetiologies. Distinct diseases including collagen vascular, infectious, and toxic etiologies may present with symptoms of myelitis and optic neuritis. There is also a clear association of myelitis and optic neuritis with otherwise typical forms of MS. In these cases, a reasonable argument can be advanced that genetic or environmental factors, or both, influence whether a demyelinating syndrome will manifest as a relatively selective disorder of the spinal cord and optic nerves.
In comparison with Western MS patients, a disproportionately high proportion of Asian patients with CNS demyelination have lesions restricted to the spinal cord and optic nerves. In Caucasian (United States) multicase MS families, early manifestations of restricted optic nerve-spinal cord involvement were found to aggregate significantly in certain families, arguing that an underlying genetic basis influences these clinical manifestations. There is also genetic evidence from studies of Japanese MS suggesting that some HLA genes may distinguish NMO from Western-type MS. Although HLA haplotypes may have a role in the pathogenesis of this syndrome, they do not yet explain any of the outstanding questions that are unique in this syndrome.
Many key questions remain unanswered. Why is there a predisposition for the spinal cord and optic nerves? Why is the brain spared? Why does necrosis occur in both gray and white matter structures of the cord? The observation that MOG, other autoantibodies, and complement deposition are found in some NMO cases suggests that humoral-mediated autoimmunity may contribute to the pathogenesis of this syndrome. If this is true, B-cell selective immunosuppressant drugs, soluble complement inhibitors, and plasma exchange may have a role in the treatment of NMO. Given the rarity of the syndrome in Western countries, randomized treatment trials will require collaboration between many centers in order to enroll sufficient numbers of patients to complete a study.
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