Axonal transection in the lesions of multiple sclerosis

BACKGROUND

Multiple sclerosis is an inflammatory demyelinating disease of the central nervous system and is the most common cause of neurologic disability in young adults. Despite antiinflammatory or immunosuppressive therapy, most patients have progressive neurologic deterioration that may reflect axonal loss. We conducted pathological studies of brain tissues to define the changes in axons in patients with multiple sclerosis.

METHODS

Brain tissue was obtained at autopsy from 11 patients with multiple sclerosis and 4 subjects without brain disease. Fourteen active multiple-sclerosis lesions, 33 chronic active lesions, and samples of normal-appearing white matter were examined for demyelination, inflammation, and axonal pathologic changes by immunohistochemistry and confocal microscopy. Axonal transection, identified by the presence of terminal axonal ovoids, was detected in all 47 lesions and quantified in 18 lesions.

RESULTS

Transected axons were a consistent feature of the lesions of multiple sclerosis, and their frequency was related to the degree of inflammation within the lesion. The number of transected axons per cubic millimeter of tissue averaged 11,236 in active lesions, 3138 at the hypocellular edges of chronic active lesions, 875 in the hypocellular centers of chronic active lesions, and less than 1 in normal-appearing white matter from the control brains.

CONCLUSIONS

Transected axons are common in the lesions of multiple sclerosis, and axonal transection may be the pathologic correlate of the irreversible neurologic impairment in this disease.

Heterogeneity of multiple sclerosis lesions: implications for the pathogenesis of demyelination

Multiple sclerosis (MS) is a disease with profound heterogeneity in clinical course, neuroradiological appearance of the lesions, involvement of susceptibility gene loci, and response to therapy. These features are supported by experimental evidence, which demonstrates that fundamentally different processes, such as autoimmunity or virus infection, may induce MS-like inflammatory demyelinating plaques and suggest that MS may be a disease with heterogeneous pathogenetic mechanisms. From a large pathology sample of MS, collected in three international centers, we selected 51 biopsies and 32 autopsies that contained actively demyelinating lesions defined by stringent criteria. The pathology of the lesions was analyzed using a broad spectrum of immunological and neurobiological markers. Four fundamentally different patterns of demyelination were found, defined on the basis of myelin protein loss, the geography and extension of plaques, the patterns of oligodendrocyte destruction, and the immunopathological evidence of complement activation. Two patterns (I and II) showed close similarities to T-cell-mediated or T-cell plus antibody-mediated autoimmune encephalomyelitis, respectively. The other patterns (III and IV) were highly suggestive of a primary oligodendrocyte dystrophy, reminiscent of virus- or toxin-induced demyelination rather than autoimmunity. At a given time point of the disease--as reflected in autopsy cases--the patterns of demyelination were heterogeneous between patients, but were homogenous within multiple active lesions from the same patient. This pathogenetic heterogeneity of plaques from different MS patients may have fundamental implications for the diagnosis and therapy of this disease.

Demyelination increases radial diffusivity in corpus callosum of mouse brain

Myelin damage, as seen in multiple sclerosis (MS) and other demyelinating diseases, impairs axonal conduction and can also be associated with axonal degeneration. Accurate assessments of these conditions may be highly beneficial in evaluating and selecting therapeutic strategies for patient management. Recently, an analytical approach examining diffusion tensor imaging (DTI) derived parameters has been proposed to assess the extent of axonal damage, demyelination, or both. The current study uses the well-characterized cuprizone model of experimental demyelination and remyelination of corpus callosum in mouse brain to evaluate the ability of DTI parameters to detect the progression of myelin degeneration and regeneration. Our results demonstrate that the extent of increased radial diffusivity reflects the severity of demyelination in corpus callosum of mouse brain affected by cuprizone treatment. Subsequently, radial diffusivity decreases with the progression of remyelination. Furthermore, radial diffusivity changes were specific to the time course of changes in myelin integrity as distinct from axonal injury, which was detected by betaAPP immunostaining and shown to be most extensive prior to demyelination. Radial diffusivity offers a specific assessment of demyelination and remyelination, as distinct from acute axonal damage.

A new rating scale for age-related white matter changes applicable to MRI and CT

BACKGROUND AND PURPOSE

MRI is more sensitive than CT for detection of age-related white matter changes (ARWMC). Most rating scales estimate the degree and distribution of ARWMC either on CT or on MRI, and they differ in many aspects. This makes it difficult to compare CT and MRI studies. To be able to study the evolution and possible effect of drug treatment on ARWMC in large patient samples, it is necessary to have a rating scale constructed for both MRI and CT. We have developed and evaluated a new scale and studied ARWMC in a large number of patients examined with both MRI and CT.

METHODS

Seventy-seven patients with ARWMC on either CT or MRI were recruited and a complementary examination (MRI or CT) performed. The patients came from 4 centers in Europe, and the scans were rated by 4 raters on 1 occasion with the new ARWMC rating scale. The interrater reliability was evaluated by using kappa statistics. The degree and distribution of ARWMC in CT and MRI scans were compared in different brain areas.

RESULTS

Interrater reliability was good for MRI (kappa=0.67) and moderate for CT (kappa=0.48). MRI was superior in detection of small ARWMC, whereas larger lesions were detected equally well with both CT and MRI. In the parieto-occipital and infratentorial areas, MRI detected significantly more ARWMC than did CT. In the frontal area and basal ganglia, no differences between modalities were found. When a fluid-attenuated inversion recovery sequence was used, MRI detected significantly more lesions than CT in frontal and parieto-occipital areas. No differences were found in basal ganglia and infratentorial areas.

CONCLUSIONS

We present a new ARWMC scale applicable to both CT and MRI that has almost equal sensitivity, except for certain regions. The interrater reliability was slightly better for MRI, as was the detectability of small lesions.

Principles of diffusion tensor imaging and its applications to basic neuroscience research

The brain contains more than 100 billion neurons that communicate with each other via axons for the formation of complex neural networks. The structural mapping of such networks during health and disease states is essential for understanding brain function. However, our understanding of brain structural connectivity is surprisingly limited, due in part to the lack of noninvasive methodologies to study axonal anatomy. Diffusion tensor imaging (DTI) is a recently developed MRI technique that can measure macroscopic axonal organization in nervous system tissues. In this article, the principles of DTI methodologies are explained, and several applications introduced, including visualization of axonal tracts in myelin and axonal injuries as well as human brain and mouse embryonic development. The strengths and limitations of DTI and key areas for future research and development are also discussed.

Remyelination in the CNS: from biology to therapy

Remyelination involves reinvesting demyelinated axons with new myelin sheaths. In stark contrast to the situation that follows loss of neurons or axonal damage, remyelination in the CNS can be a highly effective regenerative process. It is mediated by a population of precursor cells called oligodendrocyte precursor cells (OPCs), which are widely distributed throughout the adult CNS. However, despite its efficiency in experimental models and in some clinical diseases, remyelination is often inadequate in demyelinating diseases such as multiple sclerosis (MS), the most common demyelinating disease and a cause of neurological disability in young adults. The failure of remyelination has profound consequences for the health of axons, the progressive and irreversible loss of which accounts for the progressive nature of these diseases. The mechanisms of remyelination therefore provide critical clues for regeneration biologists that help them to determine why remyelination fails in MS and in other demyelinating diseases and how it might be enhanced therapeutically.

Tumor necrosis factor mediates myelin and oligodendrocyte damage in vitro

Recombinant human tumor necrosis factor (rhTNF) has been tested for its effect on myelinated cultures of mouse spinal cord tissue. As controls, recombinant human interferon gamma (rhIFN) and interleukin-2 (rhIL-2) were tested, as well as T-cell supernatants, antigalactocerebroside serum, and normal culture medium. It was found that rhTNF induced delayed-onset (18-24 hr) oligodendrocyte necrosis and a type of myelin dilatation peculiar to this system. Some nerve fibers progressed to demyelination by 72 hours. The myelin dilatation was not reversible by return to normal feeding solution for 3 days. In contrast, rhIFN, rhIL-2, T-cell supernatants, and normal medium had little or no effect on cultures. This mechanism differs from other immune-mediated mechanisms in that it appears that a physiological (not structural) demyelination occurs initially without overt destruction of the myelin sheath. These observations are relevant to the evolution of the multiple sclerosis plaque: dysfunction of ionic channels might contribute to the eventual demise of oligodendrocytes and axons in the longstanding lesion.

The AIDS dementia complex: II. Neuropathology

In order to define the histopathological substrate of the dementia that frequently complicates the acquired immune deficiency syndrome (AIDS), we analyzed the neuropathological findings in 70 autopsied adult AIDS patients, 46 of whom had suffered clinically overt dementia. Less than 10% of the brains were histologically normal. Abnormalities were found predominantly in the white matter and in subcortical structures, with relative sparing of the cortex. Their frequency and severity generally correlated well with the degree and duration of clinical dementia. Most commonly noted was diffuse pallor in the white matter, which in the pathologically milder cases was accompanied by scanty perivascular infiltrates of lymphocytes and brown-pigmented macrophages, and in the most advanced cases by clusters of foamy macrophages and multinucleated cells associated with multifocal rarefaction of the white matter. However, in nearly one third of the demented cases the histopathological findings were remarkably bland in relation to the severity of clinical dysfunction. In addition, similar mild changes were noted in over one half of the nondemented patients, consistent with subclinical involvement. Vacuolar myelopathy was found in 23 patients and was generally more common and severe in patients with advanced brain pathology. Evidence of cytomegalovirus (CMV) infection was noted in nearly one quarter of the brains and was associated with a relative abundance of microglial nodules, but correlated neither with the major subcortical neuropathology nor with the clinical dementia, indicating that CMV infection likely represented a second, superimposed process. This study establishes the AIDS dementia complex as a distinct clinical and pathological entity and, together with accumulating virological evidence, suggests that it is caused by direct LAV/HTLV-III brain infection.

A role for humoral mechanisms in the pathogenesis of Devic's neuromyelitis optica

Devic's disease [neuromyelitis optica (NMO)] is an idiopathic inflammatory demyelinating disease of the CNS, characterized by attacks of optic neuritis and myelitis. The mechanisms that result in selective localization of inflammatory demyelinating lesions to the optic nerves and spinal cord are unknown. Serological and clinical evidence of B cell autoimmunity has been observed in a high proportion of patients with NMO. The purpose of this study was to investigate the importance of humoral mechanisms, including complement activation, in producing the necrotizing demyelination seen in the spinal cord and optic nerves. Eighty-two lesions were examined from nine autopsy cases of clinically confirmed Devic's disease. Demyelinating activity in the lesions was immunocytochemically classified as early active (21 lesions), late active (18 lesions), inactive (35 lesions) or remyelinating (eight lesions) by examining the antigenic profile of myelin degradation products within macrophages. The pathology of the lesions was analysed using a broad spectrum of immunological and neurobiological markers, and lesions were defined on the basis of myelin protein loss, the geography and extension of plaques, the patterns of oligodendrocyte destruction and the immunopathological evidence of complement activation. The pathology was identical in all nine patients. Extensive demyelination was present across multiple spinal cord levels, associated with cavitation, necrosis and acute axonal pathology (spheroids), in both grey and white matter. There was a pronounced loss of oligodendrocytes within the lesions. The inflammatory infiltrates in active lesions were characterized by extensive macrophage infiltration associated with large numbers of perivascular granulocytes and eosinophils and rare CD3(+) and CD8(+) T cells. There was a pronounced perivascular deposition of immunoglobulins (mainly IgM) and complement C9neo antigen in active lesions associated with prominent vascular fibrosis and hyalinization in both active and inactive lesions. The extent of complement activation, eosinophilic infiltration and vascular fibrosis observed in the Devic NMO cases is more prominent compared with that in prototypic multiple sclerosis, and supports a role for humoral immunity in the pathogenesis of NMO. Based on this study, future therapeutic strategies designed to limit the deleterious effects of complement activation, eosinophil degranulation and neutrophil/macrophage/microglial activation are worthy of further investigation.

TNF alpha promotes proliferation of oligodendrocyte progenitors and remyelination

Here we used mice lacking tumor necrosis factor-alpha (TNF alpha) and its associated receptors to study a model of demyelination and remyelination in which these events could be carefully controlled using a toxin, cuprizone. Unexpectedly, the lack of TNF alpha led to a significant delay in remyelination as assessed by histology, immunohistochemistry for myelin proteins and electron microscopy coupled with morphometric analysis. Failure of repair correlated with a reduction in the pool of proliferating oligodendrocyte progenitors (bromodeoxyuridine-labeled NG2(+) cells) followed by a reduction in the number of mature oligodendrocytes. Analysis of mice lacking TNF receptor 1 (TNFR1) or TNFR2 indicated that TNFR2, not TNFR1, is critical to oligodendrocyte regeneration. This unexpected reparative role for TNF alpha in the CNS is important for understanding oligodendrocyte regeneration/proliferation, nerve remyelination and the design of new therapeutics for demyelinating diseases.

Why does remyelination fail in multiple sclerosis?

Multiple sclerosis is a common cause of neurological disability in young adults. The disease is complex -- its aetiology is multifactorial and largely unknown; its pathology is heterogeneous; and, clinically, it is difficult to diagnose, manage and treat. However, perhaps its most frustrating aspect is the inadequacy of the healing response of remyelination. This regenerative process generally occurs with great efficiency in experimental models, and sometimes proceeds to completion in multiple sclerosis. But as the disease progresses, the numbers of lesions in which demyelination persists increases, significantly contributing to clinical deterioration. Understanding why remyelination fails is crucial for devising effective methods by which to enhance it.

c-Jun reprograms Schwann cells of injured nerves to generate a repair cell essential for regeneration

The radical response of peripheral nerves to injury (Wallerian degeneration) is the cornerstone of nerve repair. We show that activation of the transcription factor c-Jun in Schwann cells is a global regulator of Wallerian degeneration. c-Jun governs major aspects of the injury response, determines the expression of trophic factors, adhesion molecules, the formation of regeneration tracks and myelin clearance and controls the distinctive regenerative potential of peripheral nerves. A key function of c-Jun is the activation of a repair program in Schwann cells and the creation of a cell specialized to support regeneration. We show that absence of c-Jun results in the formation of a dysfunctional repair cell, striking failure of functional recovery, and neuronal death. We conclude that a single glial transcription factor is essential for restoration of damaged nerves, acting to control the transdifferentiation of myelin and Remak Schwann cells to dedicated repair cells in damaged tissue.

Identification of autoantibodies associated with myelin damage in multiple sclerosis

The molecular mechanisms underlying myelin sheath destruction in multiple sclerosis lesions remain unresolved. With immunogold-labeled peptides of myelin antigens and high-resolution microscopy, techniques that can detect antigen-specific antibodies in situ, we have identified autoantibodies specific for the central nervous system myelin antigen myelin/oligodendrocyte glycoprotein. These autoantibodies were specifically bound to disintegrating myelin around axons in lesions of acute multiple sclerosis and the marmoset model of allergic encephalomyelitis. These findings represent direct evidence that autoantibodies against a specific myelin protein mediate target membrane damage in central nervous system demyelinating disease.

Oligodendrocytes: biology and pathology

Oligodendrocytes are the myelinating cells of the central nervous system (CNS). They are the end product of a cell lineage which has to undergo a complex and precisely timed program of proliferation, migration, differentiation, and myelination to finally produce the insulating sheath of axons. Due to this complex differentiation program, and due to their unique metabolism/physiology, oligodendrocytes count among the most vulnerable cells of the CNS. In this review, we first describe the different steps eventually culminating in the formation of mature oligodendrocytes and myelin sheaths, as they were revealed by studies in rodents. We will then show differences and similarities of human oligodendrocyte development. Finally, we will lay out the different pathways leading to oligodendrocyte and myelin loss in human CNS diseases, and we will reveal the different principles leading to the restoration of myelin sheaths or to a failure to do so.

White matter changes in schizophrenia: evidence for myelin-related dysfunction

Numerous lines of inquiry implicate connectivity as a central abnormality in schizophrenia. Myelination and factors that affect myelination, such as the function of oligodendroglia, are critical processes that could profoundly affect neuronal connectivity, especially given the diffuse distribution of oligodendrocytes and the widespread distribution of brain regions that have been implicated in schizophrenia. Multiple lines of evidence now converge to implicate oligodendroglia and myelin in schizophrenia. Imaging and neurocytochemical evidence, similarities with demyelinating diseases, age-related changes in white matter, myelin-related gene abnormalities, and morphologic abnormalities in the oligodendroglia demonstrated in schizophrenic brains are all examined in light of the hypothesis that oligodendroglial dysfunction and even death, with subsequent abnormalities in myelin maintenance and repair, contribute to the schizophrenic syndrome.

Remyelination is extensive in a subset of multiple sclerosis patients

Although spontaneous remyelination does occur in multiple sclerosis lesions, its extent within the global population with this disease is presently unknown. We have systematically analysed the incidence and distribution of completely remyelinated lesions (so-called shadow plaques) or partially remyelinated lesions (shadow plaque areas) in 51 autopsies of patients with different clinical courses and disease durations. The extent of remyelination was variable between cases. In 20% of the patients, the extent of remyelination was extensive with 60-96% of the global lesion area remyelinated. Extensive remyelination was found not only in patients with relapsing multiple sclerosis, but also in a subset of patients with progressive disease. Older age at death and longer disease duration were associated with significantly more remyelinated lesions or lesion areas. No correlation was found between the extent of remyelination and either gender or age at disease onset. These results suggest that the variable and patient-dependent extent of remyelination must be considered in the design of future clinical trials aimed at promoting CNS repair.

Magnetization transfer ratio and myelin in postmortem multiple sclerosis brain

Several quantitative magnetic resonance (MR) measures are used to investigate multiple sclerosis (MS) in vivo. Precise quantitative investigation of the histopathological correlates of such measures has, to date, been limited. This study investigates the relationship of quantitative measures of myelin content, axonal density, and gliosis with quantitative MR measures in postmortem (PM) MS tissue. MR imaging (MRI) was performed on a 1.5T scanner and T1-relaxation time (T1-RT) and magnetization transfer ratio (MTR) maps were acquired in fresh PM brain of 20 MS subjects. Myelin content, axonal counts, and the extent of gliosis all were quantified using morphometric and digital imaging techniques. MRI and pathological data were in most cases coregistered using stereotactic navigation. Using multiple regression analysis, we detected significant correlations between myelin content (Tr(myelin)) and MTR (r = -0.84, p < 0.001) and myelin content and axonal count (-0.80, p < 0.001); MTR correlated with T1-RT (r = -0.79, p < 0.001). No association was detected between the extent of gliosis and either MR measure. MTR was significantly higher in remyelinated than demyelinated lesions (means: 30.0 [standard deviation, 2.9] vs 23.8 [standard deviation, 4.3], p = 0.008). In conclusion, MTR is affected by myelin content in MS white matter.

Leuko-araiosis

Problems in the literature in the appraisal of brain deep white-matter changes are considered. The identification of the changes with Binswanger's disease alone is rejected, and evidence is reviewed that demonstrates that they are associated with cognitive impairment and, to some extent, with vascular disease. Possible causes of white-matter changes and their relationships to Alzheimer's disease are examined, and it is argued that a neutral term, exact enough to define white-matter changes, sufficient as a description or label, and demanding enough to require precise clinical and imaging descriptions is needed. We suggest herein the term "leuko-araiosis" on the basis of Greek etymology and Hippocratic usage.

Acute axonal injury in multiple sclerosis. Correlation with demyelination and inflammation

Damage to axons is taken as a key factor of disability in multiple sclerosis, but its pathogenesis is largely unknown. Axonal injury is believed to occur as a consequence of demyelination and was recently shown to be a feature even of the early disease stages. The present study was aimed at characterizing the association of axonal injury and histopathological hallmarks of multiple sclerosis such as demyelination, cellular infiltration and expression of inflammatory mediators. Therefore, axon reduction and signs of acute axonal damage were quantified in early lesion development of chronic multiple sclerosis and correlated with demyelinating activity and inflammation. Patients with secondary progressive multiple sclerosis revealed the most pronounced axonal injury, whereas primary progressive multiple sclerosis patients surprisingly showed relatively little acute axonal injury. Acute axonal damage, as defined by the accumulation of amyloid precursor protein (APP), was found to occur not only in active demyelinating but also in remyelinating and inactive demyelinated lesions with a large inter-individual variability. Only few remyelinating lesions were adjacent to areas of active demyelination. In this minority of lesions, axonal damage may have originated from the neighbourhood. APP expression in damaged axons correlated with the number of macrophages and CD8-positive T lymphocytes within the lesions, but not with the expression of tumour necrosis factor-alpha (TNF-alpha) or inducible nitric oxide synthase (iNOS). Axonal injury is therefore, at least in part, independent of demyelinating activity, and its pathogenesis may be different from demyelination. This has major implications for therapeutic strategies, which aim at preventing both demyelination and axonal loss.

Glial cytoplasmic inclusions in white matter oligodendrocytes of multiple system atrophy brains contain insoluble alpha-synuclein

Recently, alpha-synuclein was shown to be a structural component of the filaments in Lewy bodies (LBs) of Parkinson's disease (PD), dementia with LBs (DLB) as well as the LB variant of Alzheimer's disease, and this suggests that alpha-synuclein could play a mechanistic role in the pathogenesis of these disorders. To determine whether alpha-synuclein is a building block of inclusions in other neurodegenerative movement disorders, we examined brains from patients with multiple system atrophy (MSA) and detected alpha-synuclein, but not beta- or gamma-synuclein, in glial cytoplasmic inclusions (GCIs) throughout the MSA brain. In MSA white matter, alpha-synuclein-positive GCIs were restricted to oligodendrocytes, and alpha-synuclein was localized to the filaments in GCIs by immunoelectron microscopy. Finally, we demonstrated that insoluble alpha-synuclein accumulated selectively in MSA white matter with alpha-synuclein-positive GCIs. Taken together with evidence that LBs contain insoluble alpha-synuclein, our data suggest that a reduction in the solubility of alpha-synuclein may induce this protein to form filaments that aggregate into cytoplasmic inclusions, which contribute to the dysfunction or death of glial cells as well as neurons in neurodegenerative disorders with different phenotypes.

Distinct patterns of multiple sclerosis pathology indicates heterogeneity on pathogenesis

Multiple sclerosis is an inflammatory demyelinating disease of the central nervous system. The hallmark of its pathology is the demyelinated plaque with reactive glial scar formation. However, a detailed analysis of the patterns of demyelination, oligodendroglia cell pathology and the reaction of other tissue components suggests that the pathogenesis of myelin destruction in this disease may be heterogeneous. In this review we present a new classification scheme of lesional activity on the basis of the molecular composition of myelin degradation products in macrophages. When these criteria are used, different patterns of demyelination can be distinguished, including demyelination with relative preservation of oligodendrocytes, myelin destruction with concomitant and complete destruction of oligodendrocytes or primary destruction or disturbance of myelinating cells with secondary demyelination. Furthermore, in some cases a primary selective demyelination may be followed by a secondary oligodendrocyte loss in the established lesions. Finally, some extraordinarily severe conditions may result in destructive lesions with loss of myelin, oligodendrocytes, axons and astrocytes. This heterogeneity of plaque pathology is discussed in the context of recent experimental models of inflammatory demyelination, which show that different immunological pathways may lead to the formation of demyelinated plaques that reveal the diverse structural aspects described above. Our data indicate, that the demyelinated plaques of multiple sclerosis may reflect a common pathological end point of a variety of different immunological mechanisms of myelin destruction in this disease.

Structural abnormalities in the brains of human subjects who use methamphetamine

We visualize, for the first time, the profile of structural deficits in the human brain associated with chronic methamphetamine (MA) abuse. Studies of human subjects who have used MA chronically have revealed deficits in dopaminergic and serotonergic systems and cerebral metabolic abnormalities. Using magnetic resonance imaging (MRI) and new computational brain-mapping techniques, we determined the pattern of structural brain alterations associated with chronic MA abuse in human subjects and related these deficits to cognitive impairment. We used high-resolution MRI and surface-based computational image analyses to map regional abnormalities in the cortex, hippocampus, white matter, and ventricles in 22 human subjects who used MA and 21 age-matched, healthy controls. Cortical maps revealed severe gray-matter deficits in the cingulate, limbic, and paralimbic cortices of MA abusers (averaging 11.3% below control; p < 0.05). On average, MA abusers had 7.8% smaller hippocampal volumes than control subjects (p < 0.01; left, p = 0.01; right, p < 0.05) and significant white-matter hypertrophy (7.0%; p < 0.01). Hippocampal deficits were mapped and correlated with memory performance on a word-recall test (p < 0.05). MRI-based maps suggest that chronic methamphetamine abuse causes a selective pattern of cerebral deterioration that contributes to impaired memory performance. MA may selectively damage the medial temporal lobe and, consistent with metabolic studies, the cingulate-limbic cortex, inducing neuroadaptation, neuropil reduction, or cell death. Prominent white-matter hypertrophy may result from altered myelination and adaptive glial changes, including gliosis secondary to neuronal damage. These brain substrates may help account for the symptoms of MA abuse, providing therapeutic targets for drug-induced brain injury.

Brain abnormalities in neuromyelitis optica

BACKGROUND

Neuromyelitis optica (NMO) is a severe demyelinating disease defined principally by its tendency to selectively affect optic nerves and the spinal cord causing recurrent attacks of blindness and paralysis. Contemporary diagnostic criteria require absence of clinical disease outside the optic nerve or spinal cord. We have, however, frequently encountered patients with a well-established diagnosis of NMO in whom either asymptomatic or symptomatic brain lesions develop suggesting that the diagnostic criteria for NMO should be revised.

OBJECTIVE

To describe the magnetic resonance image (MRI) brain findings in NMO.

DESIGN

Observational, retrospective case series. Patients We ascertained patients through a clinical biospecimens database of individuals with definite or suspected NMO. We included patients who (1) satisfied the 1999 criteria of Wingerchuk et al for NMO except for the absolute criterion of lacking symptoms beyond the optic nerve and spinal cord and the supportive criterion of having a normal brain MRI at onset; (2) had MRI evidence of a spinal cord lesion extending 3 vertebral segments or more (the most specific nonserological feature to differentiate NMO from MS); and (3) were evaluated neurologically and by brain MRI at the Mayo Clinic.

MAIN OUTCOME MEASURES

Magnetic resonance images were classified as normal or as abnormal with either nonspecific, multiple sclerosis-like or atypical abnormalities. We evaluated whether brain lesions were symptomatic and analyzed the neuropathologic features of a single brain biopsy specimen.

RESULTS

Sixty patients (53 women [88%]) fulfilled these inclusion criteria. The mean +/- SD age at onset was 37.2 +/- 18.4 years and the mean +/- SD duration of follow-up was 6.0 +/- 5.6 years. Neuromyelitis optica-IgG was detected in 41 patients (68%). Brain MRI lesions were detected in 36 patients (60%). Most were nonspecific, but 6 patients (10%) had multiple sclerosis-like lesions, usually asymptomatic. Another 5 patients (8%), mostly children, had diencephalic, brainstem or cerebral lesions, atypical for multiple sclerosis. When present, symptoms of brain involvement were subtle, except in 1 patient who was comatose and had large cerebral lesions.

CONCLUSIONS

Asymptomatic brain lesions are common in NMO, and symptomatic brain lesions do not exclude the diagnosis of NMO. These observations justify revision of diagnostic criteria for NMO to allow for brain involvement.

White matter changes in Alzheimer's disease: a focus on myelin and oligodendrocytes

Alzheimer's disease (AD) is conceptualized as a progressive consequence of two hallmark pathological changes in grey matter: extracellular amyloid plaques and neurofibrillary tangles. However, over the past several years, neuroimaging studies have implicated micro- and macrostructural abnormalities in white matter in the risk and progression of AD, suggesting that in addition to the neuronal pathology characteristic of the disease, white matter degeneration and demyelination may be also important pathophysiological features. Here we review the evidence for white matter abnormalities in AD with a focus on myelin and oligodendrocytes, the only source of myelination in the central nervous system, and discuss the relationship between white matter changes and the hallmarks of Alzheimer's disease. We review several mechanisms such as ischemia, oxidative stress, excitotoxicity, iron overload, Aβ toxicity and tauopathy, which could affect oligodendrocytes. We conclude that white matter abnormalities, and in particular myelin and oligodendrocytes, could be mechanistically important in AD pathology and could be potential treatment targets.