Morphology of demyelination in the human central nervous system

The principles of the neuropathological classification of disorders of central nervous system myelin are recalled. They are illustrated by a few selected examples. Dysmyelination is characterized by the production of an abnormal and unstable myelin sheath; it is often associated with hypomyelination (paucity of myelin formation) and is due to metabolic disorders. It is the main process in leukodystrophies. Storage of different lipids (e.g. sulfatides, long-chain fatty acids) or associated pathology of various cell types (in Alexander's disease, for example) are used for classifying these disorders. Biochemical and genetic characterizations are presently ongoing. Demyelination is the destruction of apparently normal myelin. It is often followed by remyelination. Our present knowledge on the neuropathology of multiple sclerosis, the most common demyelinating disease, is summarized. Cell-mediated demyelination affects the myelin sheaths for an obscure reason. The causes of the multifocal and sharply demarcated plaques, and of the fading of the remyelination process at the edge of some plaques, are not clear. A few examples of demyelinating diseases of known etiology and of various mechanisms are given. The similarities between acute disseminated leukoencephalitis and experimental autoimmune encephalitis are stressed. In progressive multifocal leukoencephalopathy, chronic infection of oligodendrocytes by JC virus induces poorly defined areas of demyelination. In AIDS, the pathogenesis of the myelin change is unclear. Macrophages may be responsible. Toxic and vascular disorders provide also good models for the understanding of mechanisms of demyelination.     

Remyelination follows antibody-induced central nervous system demyelination

Remyelination after anti-galactocerebroside-induced demyelination in the guinea pig optic nerve was evident 17 days after the onset of demyelination. The tempo of remyelination was uniform for large- and small-diameter axons and progressed, with compaction and thickening of myelin sheaths. Demyelinated axons were found interspersed among remyelinated fibers and were consistently separated from oligodendrocytes by astrocytic processes. These findings indicate that central nervous system remyelination may occur after in vivo antibody-induced demyelination, but that new myelin formation may be limited by mechanical interference from astrocytic processes.     

Aggressive central nervous system demyelination in an adolescent

A 15-year-old boy diagnosed with a severe, active, and aggressive form of multiple sclerosis (MS) failed conventional, evidence-based therapy. The optimal treatment of the child or adolescent failing federally approved therapy for MS is unclear, similar to the situation in adults. This case history demonstrates that aggressive immunosuppression might be of at least short-term value in controlling disease acutely in an adolescent, as in adults with MS, when evidence-based therapies do not provide an adequate response.     

Myelination, demyelination and re-myelination in the central nervous system

The myelin sheaths that surround axons in the CNS are made and maintained by oligodendrocytes. These glial cells can form variable numbers of myelin segments (internodules): from 1 to 200 so that when one oligodendrocyte is destroyed with preservation of the axon, many internodules can be lost, constituting a demyelinating process. As a consequence of the destruction of myelin and sheath cells a rapid and abundant cell response takes place. The response is made up by resident (microglia) and haematogenous phagocytes which phagocytose myelin and cellular debris leaving the axons demyelinated. Demyelinated axons may either stay demyelinated and clumped together or they may be separated by astrocytic processes, yet they can be remyelinated. The occurrence of remyelination depends upon the intensity and time of exposition to the demyelinating agent. Remyelination in the CNS with complete restoration of conduction may be made by oligodendrocytes or Schwann cells which invade the CNS when astrocytes are destroyed.     

Inhibition of Piezo1 attenuates demyelination in the central nervous system

Piezo1 is a mechanosensitive ion channel that facilitates the translation of extracellular mechanical cues to intracellular molecular signaling cascades through a process termed, mechanotransduction. In the central nervous system (CNS), mechanically gated ion channels are important regulators of neurodevelopmental processes such as axon guidance, neural stem cell differentiation, and myelination of axons by oligodendrocytes. Here, we present evidence that pharmacologically mediated overactivation of Piezo1 channels negatively regulates CNS myelination. Moreover, we found that the peptide GsMTx4, an antagonist of mechanosensitive cation channels such as Piezo1, is neuroprotective and prevents chemically induced demyelination. In contrast, the positive modulator of Piezo1 channel opening, Yoda-1, induces demyelination and neuronal damage. Using an ex vivo murine-derived organotypic cerebellar slice culture model, we demonstrate that GsMTx4 attenuates demyelination induced by the cytotoxic lipid, psychosine. Importantly, we confirmed the potential therapeutic effects of GsMTx4 peptide in vivo by co-administering it with lysophosphatidylcholine (LPC), via stereotactic injection, into the cerebral cortex of adult mice. GsMTx4 prevented both demyelination and neuronal damage usually caused by the intracortical injection of LPC in vivo; a well-characterized model of focal demyelination. GsMTx4 also attenuated both LPC-induced astrocyte toxicity and microglial reactivity within the lesion core. Overall, our data suggest that pharmacological activation of Piezo1 channels induces demyelination and that inhibition of mechanosensitive channels, using GsMTx4, may alleviate the secondary progressive neurodegeneration often present in the latter stages of demyelinating diseases.     

Experimental models of virus-induced demyelination of the central nervous system

One of the arguments in favor of a viral pathogenesis for multiple sclerosis is the existence of several experimental and natural animal models of virus-induced primary demyelination. This review deals comprehensively with such models. Well-known examples of demyelinating viral infections in their natural host are JHM, Theiler, visna, and canine distemper encephalomyelitides. Recent reports of experimental murine infections with pathogens such as vesicular stomatitis, Chandipura, herpes simplex, Venezuelan equine encephalomyelitis, and Semliki Forest viruses are also discussed. The thrust of the review is to include viral models suspected of producing primary demyelination on an immunopathological basis.     

The role of interleukin-6 in central nervous system demyelination

正Demyelination of the central nervous system(CNS)is a hallmark of multiple sclerosis(MS),chronic inflammatory and neurodegenerative disease.Chronic demyelination favors neurodegeneration of denuded axons,which is a major cause of irreversible neuronal deficits and disability in MS patients(Lucchinetti et al.,2000).MS remains an incurable disease,despite formida-     

POEMS Syndrome with central and peripheric nervous system demyelination

POEMS syndrome is characterized by polyneuropathy, organomegaly, endocrinopathy, monoclonal protein and skin changes. This polyneuropathy belongs to the chronic inflammatory demyelinating polyradiculoneuropathies (CIDP) group. Sporadic reports have emphasized the clinical association between CIDP and central nervous system (CNS) demyelination, but as far as we know not in the context of POEMS syndrome. We report the case of a 67 years old patient who developed POEMS syndrome associated to Castleman's disease, characterized by demyelinating polyradiculoneuropathy, hepatosplenomegaly, mediastinal and supraclavicular adenopathies and monoclonal IgG lambda gammapathy. Cranial magnetic resonance imaging disclosed diffuse alteration of the cerebral white matter highly suggestive of demyelination. CNS demyelination can be another feature of POEMS syndrome. Cranial MRI should be performed in patients with POEMS syndrome in order to verify this new feature.     

Acute combined central and peripheral nervous system demyelination in children

Reports of acute combined central and peripheral nervous system acquired inflammatory demyelination are rare in children. This study aimed to (1) define the clinical features and prognoses of patients with this entity; and (2) compare these patients with children presenting isolated acute central or peripheral nervous system demyelination. A retrospective chart review of 523 children with central or peripheral nervous system demyelination hospitalized between 1993-2006 was undertaken. Among these, 93 fulfilled criteria (clinical features and positive magnetic resonance imaging or electromyography/nerve conduction studies) for either acute central (n = 37; 39.8%) or peripheral (n = 43; 46%) nervous system demyelination, or a combination of the two (n = 13; 14%). Significant differences between groups were evident for age (median, 10 versus 7 versus 11 years, respectively; P = 0.047), admission to pediatric intensive care unit (8% versus 30% versus 58%, respectively; P = 0.001), length of hospital stay (median, 8 versus 9 versus 29 days, respectively; P < 0.001), treatment with steroids (52% versus 7% versus 75%, respectively; P < 0.001) and immunoglobulins (11% versus 81% versus 75%, respectively; P < 0.001), and poor evolution (3% versus 12% versus 54%, respectively; P = 0.002). This entity in children is not rare, and has a poorer outcome than isolated central or peripheral nervous system demyelination. Assessment is needed for a better understanding of risk factors, etiologies, management, and prognosis.     

Death receptor signalling in central nervous system inflammation and demyelination

Death receptors (DRs) are members of the tumor necrosis factor receptor (TNF-R) superfamily that are characterised by the presence of a conserved intracellular death domain and are able to trigger a signalling pathway leading to apoptosis. Strong evidence suggests that DRs contribute to the pathology of tissue destructive diseases, including multiple sclerosis (MS), the most common inflammatory demyelinating disease of the central nervous system (CNS). Here, we review the evidence supporting a role for DRs in MS pathology and its implications for the development of therapeutic strategies for MS and other demyelinating pathologies of the CNS.     

The role of intedeukin-6 in central nervous system demyelination

Demyelination of the central nervous system (CNS) is a hallmark of multiple sclerosis (MS),chronic inflammatory and neurodegenerative disease.Chronic demyelination favors neurodegeneration of denuded axons,which is a major cause of irreversible neuronal deficits and disability in MS patients (Lucchinetti et al.,2000).MS remains an incurable disease,despite formidable global research efforts.     

Effector pathways in immune mediated central nervous system demyelination.

Multiple sclerosis is generally regarded to be a primarily T-cell driven disease. Recent evidence has refocused interest on antibodies. Adhesion molecules, matrix metalloproteinases, chemokines and cytokines, and nitric oxide and oxygen metabolites all participate in the amplification and effector stages of the disease.     

Post-streptococcal autoimmune disorders of the central nervous system

Group A Streptococcus can induce autoimmune disease in humans with particular involvement of the heart, joints, and brain. The spectrum of post-streptococcal disease of the central nervous system (CNS) has been widened recently and includes movement disorders (chorea, tics, dystonia, and Parkinsonism), psychiatric disorders (particularly emotional disorders), and associated sleep disorders. Neuroimaging and pathological studies indicate that the most vulnerable brain region is the basal ganglia. The immunopathogenesis of the disease is incompletely defined, and although there is some support for autoantibody-mediated disease, several conflicting studies cast doubt on the autoantibody hypothesis. It has been speculated that post-streptococcal autoimmunity has a role in common neuropsychiatric disease but the evidence is conflicting and routine screening of patients with Tourette syndrome and obsessive-compulsive disorder for post-streptococcal autoimmune abnormalities is not be recommended at present. However, post-streptococcal disorders of the CNS remain a useful model of neuropsychiatric disease, which may improve our understanding of abnormal movements and behaviours in children.     

Post-streptococcal autoimmune disorders of the central nervous system

PURPOSE OF REVIEW: Autoimmune disease has long been intertwined with investigations of infectious causes. Antibodies that are formed against an infectious agent can, through the process of molecular mimicry, also recognize healthy cells. When this occurs, the immune system erroneously destroys the healthy cells causing autoimmune disease in addition to appropriately destroying the offending infectious agent and attenuating the infectious process. The first infectious agent shown to cause a post-infectious autoimmune disorder in the central nervous system was Streptococcus pyogenes in Sydenham's chorea. The present review summarizes the most recent published findings of central nervous system diseases that have evidence of a post-streptococcal autoimmune etiology. RECENT FINDINGS: Sydenham's chorea and other central nervous system illnesses that are hypothesized to have a post-streptococcal autoimmune etiology appear to arise from targeted dysfunction of the basal ganglia. PANDAS (pediatric autoimmune disorders associated with streptococcal infections) is the acronym applied to a subgroup of children with obsessive-compulsive disorder or tic disorders occurring in association with streptococcal infections. In addition, there are recent reports of dystonia, chorea encephalopathy, and dystonic choreoathetosis occurring as sequelae of streptococcal infection. Investigators have begun to isolate and describe antistreptococcal-antineuronal antibodies as well as possible genetic markers in patients who are susceptible to these illnesses. SUMMARY: Clinical and research findings in both immunology and neuropsychiatry have established the existence of post-streptococcal neuropsychiatric disorders and are beginning to shed light on possible pathobiologic processes.     

Neuroimaging in postinfectious demyelination and nutritional disorders of the central nervous system

The myelin sheath and oligodendrocytes in the brain may be damaged by autoimmune-mediated inflammatory processes secondary to postinfectious demyelination or nutritional and vitamin deficiency. This article describes acute disseminated encephalomyelitis, acute hemorrhagic leukoencephalitis, acute necrotizing encephalopathy, and tumefactive demyelination as well as osmotic demyelination, Wernicke encephalopathy, Marchiafava-Bignami disease, and subacute combined degeneration of the spinal cord. Although some characteristic MR imaging features allow radiologists to suggest a diagnosis, these may overlap, and images should be interpreted in light of clinical symptoms and laboratory investigations.     

Corticosteroids delay remyelination of experimental demyelination in the rodent central nervous system

High dose corticosteroid (CS) administration is a common mode of therapy in treatment of acute relapses in multiple sclerosis (MS) but the effects of CS on remyelination and the cellular mechanisms mediating this repair process are controversial. We have examined CS effects on repair of toxin-induced demyelinating lesions in the adult rat spinal cord. Corticosteroids reduced the extent of oligodendrocyte remyelination at 1 month post lesion (whereas Schwann-cell mediated repair was unaffected). However, CS did not cause permanent impairment of remyelination as lesions were fully remyelinated at 2 months after cessation of treatment. The delay in oligodendrocyte mediated repair could be attributed to inhibition of differentiation of oligodendrocyte progenitor cells (OPCs) into oligodendrocytes, with no effect of CS treatment observed on OPC colonisation of the lesions. No differences were observed in animals treated with methylprednisolone succinate alone or with a subsequent prednisone taper indicating that CS effects occur at an early stage of repair. The potential consequences of delayed remyelination in inflammatory lesions are discussed.