The pathology of multiple sclerosis--fact, fiction and hypothesis

An Overview of Venous Abnormalities Related to the Development of Lesions in Multiple Sclerosis

The etiology of multiple sclerosis (MS) is currently understood to be autoimmune. However, there is a long history and growing evidence for disrupted vasculature and flow within the disease pathology. A broad review of the literature related to vascular effects in MS revealed a suggestive role for abnormal flow in the medullary vein system. Evidence for venous involvement in multiple sclerosis dates back to the early pathological work by Charcot and Bourneville, in the mid-nineteenth century. Pioneering work by Adams in the 1980s demonstrated vasculitis within the walls of veins and venules proximal to active MS lesions. And more recently, magnetic resonance imaging (MRI) has been used to show manifestations of the central vein as a precursor to the development of new MS lesions, and high-resolution MRI using Ferumoxytol has been used to reveal the microvasculature that has previously only been demonstrated in cadaver brains. Both approaches may shed new light into the structural changes occurring in MS lesions. The material covered in this review shows that multiple pathophysiological events may occur sequentially, in parallel, or in a vicious circle which include: endothelial damage, venous collagenosis and fibrin deposition, loss of vessel compliance, venous hypertension, perfusion reduction followed by ischemia, medullary vein dilation and local vascular remodeling. We come to the conclusion that a potential source of MS lesions is due to locally disrupted flow which in turn leads to remodeling of the medullary veins followed by endothelial damage with the subsequent escape of glial cells, cytokines, etc. These ultimately lead to the cascade of inflammatory and demyelinating events which ensue in the course of the disease.

Revealing vascular abnormalities and measuring small vessel density in multiple sclerosis lesions using USPIO

BACKGROUND AND PURPOSE

Multiple Sclerosis (MS) is a progressive, inflammatory, neuro-degenerative disease of the central nervous system (CNS) characterized by a wide range of histopathological features including vascular abnormalities. In this study, an ultra-small superparamagnetic iron oxide (USPIO) contrast agent, Ferumoxytol, was administered to induce an increase in susceptibility for both arteries and veins to help better reveal the cerebral microvasculature. The purpose of this work was to examine the presence of vascular abnormalities and vascular density in MS lesions using high-resolution susceptibility weighted imaging (SWI).

METHODS

Six subjects with relapsing remitting MS (RRMS, age = 47.3 ± 11.8 years with 3 females and 3 males) and fourteen age-matched healthy controls were scanned at 3 T with SWI acquired before and after the infusion of Ferumoxytol. Composite data was generated by registering the FLAIR data to the high resolution SWI data in order to highlight the vascular information in MS lesions. Both the central vein sign (CVS) and, a new measure, the multiple vessel sign (MVS) were identified, along with any vascular abnormalities, in the lesions on pre- and post-contrast SWI-FLAIR fusion data. The small vessel density within the periventricular normal-appearing white matter (NAWM) and the periventricular lesions were compared for all subjects.

RESULTS

Averaged across two independent raters, a total of 530 lesions were identified across all patients. The total number of lesions with vascularity on pre- and post-contrast data were 287 and 488, respectively. The lesions with abnormal vascular behavior were broken up into following categories: small lesions appearing only at the vessel boundary; dilated vessels within the lesions; and developmental venous angiomas. These vessel abnormalities observed within lesions increased from 55 on pre-contrast data to 153 on post-contrast data. Finally, across all the patients, the periventricular lesional vessel density was significantly higher (p < 0.05) than that of the periventricular NAWM.

CONCLUSIONS

By inducing a super-paramagnetic susceptibility in the blood using Ferumoxytol, the vascular abnormalities in the RRMS patients were revealed and small vessel densities were obtained. This approach has the potential to monitor the venous vasculature present in MS lesions, catalogue their characteristics and compare the vascular structures spatially to the presence of lesions. These enhanced vascular features may provide new insight into the pathophysiology of MS.

The Gray Degeneration of the Brain and Spinal Cord: A Story of the Once Favored Diagnosis With Subsequent Vessel-Based Etiopathological Studies in Multiple Sclerosis

In 1857, French-Austrian psychiatrist Bénédict Augustin Morel (1809-1873) published his infamous though highly successful Traité des dégénérescences physiques, intellectuelles et morales de l'espèce humaine, which was fully dedicated to the social problem of "degeneration" and its psychiatric and neurological underpinnings. European psychiatrists, neurologists, and pathologists integrated Morel's approach into their neuropsychiatric theories and searched for the somatic and morphological alterations in the human brain, as did the versatile pupil of Rudolph Virchow (1821-1902), Georg Eduard von Rindfleisch (1836-1908), in his Lehrbuch der pathologischen Gewebelehre (1867). This can be seen as a starting point of research into the vascular genesis of "multiple sclerosis" by observing that the changes of blood vessels and nerve elements could be the result of inflammation and increased blood flow. We examine the waxing and waning of a 19th century diagnostic condition, which fell out of favor and resurfaced during the 20th century.

Women who contributed to past research in multiple sclerosis

BACKGROUND

The history of multiple sclerosis (MS) is dominated by the discoveries of famous men. However, women would like to feel part of the story and to know that women have contributed to MS research.

OBJECTIVE

To identify women who contributed to the history of discovery in MS.

METHOD

This was a personal survey from my knowledge of previous work.

RESULTS

There were no women participants in the early stages of MS research. However, since 1950 there are many women who have contributed to MS research. In the 20th century, there were famous women who contributed to the scientific fields that form the basis of MS research. In the 21st century, more women participate in MS research but studies suggest that they are under-represented in positions of prominence.

CONCLUSION

Women have been part of the effort to understand MS, but are not well recognized.

Inorganic mercury in human astrocytes, oligodendrocytes, corticomotoneurons and the locus ceruleus: implications for multiple sclerosis, neurodegenerative disorders and gliomas

Neurotoxic metals have been implicated in the pathogenesis of multiple sclerosis, neurodegenerative disorders and brain tumours but studies of the location of heavy metals in human brains are rare. In a man who injected himself with metallic mercury the cellular location of mercury in his brain was studied after 5 months of continuous exposure to inorganic mercury arising from metallic mercury deposits in his organs. Paraffin sections from the primary motor and sensory cortices and the locus ceruleus in the pons were stained with autometallography to detect inorganic mercury and combined with glial fibrillary acidic protein immunohistochemistry to identify astrocytes. Inorganic mercury was found in grey matter subpial, interlaminar, protoplasmic and varicose astrocytes, white matter fibrous astrocytes, grey but not white matter oligodendrocytes, corticomotoneurons and some locus ceruleus neurons. In summary, inorganic mercury is taken up by five types of human brain astrocytes, as well as by cortical oligodendrocytes, corticomotoneurons and locus ceruleus neurons. Mercury can induce oxidative stress, stimulate autoimmunity and damage DNA, mitochondria and lipid membranes, so its location in these CNS cells suggests it could play a role in the pathogenesis of multiple sclerosis, neurodegenerative conditions such as Alzheimer's disease and amyotrophic lateral sclerosis, and glial tumours.

Ultrasonographic evaluation of cerebral arterial and venous haemodynamics in multiple sclerosis: a case-control study

Objective

Although recent studies excluded an association between Chronic Cerebrospinal Venous Insufficiency and Multiple Sclerosis (MS), controversial results account for some cerebrovascular haemodynamic impairment suggesting a dysfunction of cerebral autoregulation mechanisms. The aim of this cross-sectional, case-control study is to evaluate cerebral arterial inflow and venous outflow by means of a non-invasive ultrasound procedure in Relapsing Remitting (RR), Primary Progressive (PP) Multiple Sclerosis and age and sex-matched controls subjects.

Material and Methods

All subjects underwent a complete extra-intracranial arterial and venous ultrasound assessment with a color-coded duplex sonography scanner and a transcranial doppler equipment, in both supine and sitting position by means of a tilting chair. Basal arterial and venous morphology and flow velocities, postural changes in mean flow velocities (MFV) of middle cerebral arteries (MCA), differences between cerebral venous outflow (CVF) in clinostatism and in the seated position (ΔCVF) and non-invasive cerebral perfusion pressure (CPP) were evaluated.

Results

85 RR-MS, 83 PP-MS and 82 healthy controls were included. ΔCVF was negative in 45/85 (52.9%) RR-MS, 63/83 (75.9%) PP-MS (p = 0.01) and 11/82 (13.4%) controls (p<0.001), while MFVs on both MCAs in sitting position were significantly reduced in RR-MS and PP-MS patients than in control, particularly in EDSS≥5 subgroup (respectively, 42/50, 84% vs. 66/131, 50.3%, p<0.01 and 48.3±2 cm/s vs. 54.6±3 cm/s, p = 0.01). No significant differences in CPP were observed within and between groups.

Conclusions

The quantitative evaluation of cerebral blood flow (CBF) and CVF and their postural dependency may be related to a dysfunction of autonomic nervous system that seems to characterize more disabled MS patients. It's not clear whether the altered postural control of arterial inflow and venous outflow is a specific MS condition or simply an “epiphenomenon” of neurodegenerative events.

Internal jugular vein blood flow in multiple sclerosis patients and matched controls

The aim of the study was to investigate the Internal Jugular Veins dynamics using contrast enhanced ultrasonography in Multiple Sclerosis patients, clinically isolated syndrome patients and healthy controls. Contrast enhanced ultrasonography imaging of the Internal Jugular Vein was performed in fifty-eight patients with Multiple Sclerosis, seven clinically isolated syndrome patients and in thirteen healthy controls. Time-intensity curves were quantified using a semi-automated method and compared with clinical disease outcomes. Wash-out parameters were calculated and six Time-intensity curves shapes were created. Significantly reduction of wash-out rate in Internal Jugular Veins was detected in Multiple Sclerosis patients compared to healthy controls [22.2% (2.7%–65.9%) vs. 33.4% (16.2%–76.8%); P<0.005]. Internal Jugular Vein enhancement was heterogeneous in patients with Multiple Sclerosis and consisted of slow wash-out Time-intensity curves shapes, compared with almost only one type of Time-intensity curves shape in control subjects that correspond to fast enhancement and fast wash-out. The vein wash-in parameters were similar in Multiple Sclerosis group compared with controls. A significant correlation was found between Internal Jugular Vein wash-out and level of disability (R = −0.402, p<0.05). Contrast enhanced ultrasonography of the Internal Jugular Vein with time intensity curve analysis revealed alterations of cerebral venous outflow in Multiple Sclerosis patients, however mechanisms that determine this condition remains unclear.

Chronic cerebrospinal venous insufficiency and multiple sclerosis: history and background

Multiple sclerosis (MS) is a chronic inflammatory disorder of the central nervous system (CNS) most commonly characterized by focal areas of myelin destruction, inflammation and axonal transection. The multicentric inflammation and demyelination of the brain and spinal cord are associated with variable neurologic symptoms ranging from mild dysfunction to debilitating. Typically, these symptoms are marked by episodes of clinical worsening followed by improvement. The cause of this disease remains unclear currently, but the underlying etiology is generally considered to be immunologically based. Other factors, including genetic, environmental and infectious influences have been implicated, as well. Now recent studies have proposed that extracranial venous obstruction, termed chronic cerebrospinal venous insufficiency (CCSVI) may have a role in the pathogenesis of MS or many of its associated clinical manifestations. It is postulated that venous narrowing affecting one or more of the jugular veins and/or the azygous vein in the chest may be responsible for abnormal blood flow in the veins draining the brain and spinal cord. The abnormal flow may initiate and/or sustain a local inflammatory response at the blood-brain barrier that promote pathological changes within the CNS. This review presents the history of the relationship between the vascular system and MS and explores the background of basic and clinical investigations that led to the concept of CCSVI.

Anomalous venous blood flow and iron deposition in multiple sclerosis

Multiple sclerosis (MS) is primarily an autoimmune disorder of unknown origin. This review focuses iron overload and oxidative stress as surrounding cause that leads to immunomodulation in chronic MS. Iron overload has been demonstrated in MS lesions, as a feature common with other neurodegenerative disorders. However, the recent description of chronic cerebrospinal venous insufficiency (CCSVI) associated to MS, with significant anomalies in cerebral venous outflow hemodynamics, permit to propose a parallel with chronic venous disorders (CVDs) in the mechanism of iron deposition. Abnormal cerebral venous reflux is peculiar to MS, and was not found in a miscellaneous of patients affected by other neurodegenerative disorders characterized by iron stores, such as Parkinson's, Alzheimer's, amyotrophic lateral sclerosis. Several recently published studies support the hypothesis that MS progresses along the venous vasculature. The peculiarity of CCSVI-related cerebral venous blood flow disturbances, together with the histology of the perivenous spaces and recent findings from advanced magnetic resonance imaging techniques, support the hypothesis that iron deposits in MS are a consequence of altered cerebral venous return and chronic insufficient venous drainage.

Assessing structure and function of the afferent visual pathway in multiple sclerosis and associated optic neuritis

The afferent visual pathway is commonly affected in MS. Assessment of the afferent visual pathway using clinical, imaging and electrophysiological methods not only provides insights into the pathophysiology of MS, but also provides a method of investigating potential therapeutic measures in MS. This review summarises the various assessment methods, in particular imaging techniques of the visual pathway. Retinal nerve fibre layer (RNFL) thickness is usually reduced following an episode of optic neuritis. Techniques such as optical coherence tomography, scanning laser polarimetry, and confocal scanning laser ophthalmoscopy are used to quantify RNFL thickness. MRI of the optic nerve is not routinely used in the diagnosis of MS or optic neuritis, but is valuable in atypical cases and in research. T2- weighted images of the optic nerve usually show the hyperintense lesion in optic neuritis and gadolinium enhancement is seen in the acute attack. Quantifying atrophy of the optic nerve using MRI gives an indication of the degree of axonal loss. Magnetization transfer ratio (MTR) of the optic nerve provides an indication of myelination. Diffusion tensor imaging (DTI) of the optic nerve and optic radiation provide information about the integrity of the visual white matter tracts. Functional MRI following visual stimulation is used to assess the contribution of cortical reorganisation to functional recovery following optic neuritis. Investigations including logMAR visual acuity, Sloan contrast acuity, Farnsworth- Munsell 100-hue colour vision tests and Humphrey perimetry provide detailed quantitative information on different aspects of visual function. Visual evoked potentials identify conduction block or delay reflecting demyelination. These collective investigative methods have advanced knowledge of pathophysiological mechanisms in MS and optic neuritis. Relevant ongoing studies and future directions are discussed.

[Case of suspected multiple sclerosis with transcallosal lesions involving the upper surface of the corpus callosum]

A 26-year-old woman noticed gradually progressive, right lower leg weakness over a 1.5-month period. Neurological examination revealed right hemiparesis with slightly increased deep tendon reflexes, Babinski's sign on the right side, loss of position sense in the right leg, and slight loss of superficial sensation in the right toes. MR FLAIR images showed a high intensity area measuring 5 x 2 x 3 cm in the left frontal lobe, extending to the outer surface of the body of the corpus callosum and the adjacent right cingulate gyrus. Gadolinium enhancement was seen along the cortex and the outer surface of the body of the corpus callosum. CSF findings showed no pleocytosis, a protein content of 32 mg/dl, a sugar level of 85 mg/dl, and an IgG index of 0.46. The biopsy specimen obtained from the superior frontal gyrus showed perivascular cuffing of T-lymphocytes and some B-lymphocytes, as well as multiple small foci of demyelination. Starting on the second day of admission, the patient was treated with methylprednisolone pulse therapy (1,000 mg/day for 3 days); she was then switched to oral prednisolone (20 mg/day). Thereafter, the patient had two clinical relapses: one was due to a lesion in the dorsal part of the medulla oblongata associated with a disturbance of deep sensation in both hands, and the other was due to a lesion involving the right internal capsule, the globus pallidus, and the caudate nucleus associated with left facial nerve palsy. Visual evoked potentials suggested a demyelinating lesion in the right optic nerve. We suspected a diagnosis of multiple sclerosis based on the presence of more than two clinical episodes of neurological deficits with identifiable lesions on MRI. Multiple sclerosis should be considered in the differential diagnosis of lesions located in the outer part of the corpus callosum and transcallosal bilateral hemispheres on MRI, even though inner callosal lesions are common in multiple sclerosis.

Reduced frequency of memory CD8+ T lymphocytes in cerebrospinal fluid and blood of patients with multiple sclerosis

Three color flow cytometry was used to analyze immunoregulatory lymphocyte subsets in peripheral blood (PB) and cerebrospinal fluid (CSF) of 21 patients with multiple sclerosis (MS) and 15 age-matched healthy control subjects. Two cell surface antigens associated with T lymphocyte memory and activation, CD45R0 and CD29, were analyzed on the CD4+ and CD8+ subpopulations, respectively. A selective decrease in the expression of the CD45R0 isoform among CD8+ cells was noted in both PB (p < 0.005) and CSF (p > 0.0001) of patients with MS as compared with the control group while the expression of CD29 did not differ between the groups. These changes could indicate a defective differentiation into mature memory CD8+ T lymphocytes in patients with MS. Furthermore, the CD3+CD16/56+ T lymphocyte subset capable of mediating NK cell-like activities was investigated. Although this cell population is quantitatively small, a significant reduction of the proportion of this cell type was detected in both BP and CSF of the MS group compared with the controls (p < 0.01 and p > 0.001, respectively). Further studies are needed to establish the role of these observations in the pathogenesis of MS.

Does a retrovirally encoded superantigen cause multiple sclerosis?

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The etiology of multiple sclerosis: a new and extended vascular-ischemic model

It is hypothesized that multiple sclerosis is a disease of the cerebro-vascular system. The basic defect is visualized as a wound in the CNS due to a focal hypertension of genetically susceptible vessels which results in vascular injury and the initiation of a series of biochemical and physiological events culminating in an ischemic hypoxia leading to demyelination and a secondary damaging process associated with the immune system.

Immune mechanisms in the pathogenesis of demyelinating diseases

The loss of myelin which characterises many human and experimental demyelinating diseases, among them multiple sclerosis, is thought to be immune mediated, but the precise mechanisms responsible remain unknown despite intense research. Normally, myelin in the central nervous system (CNS) is protected from systemic immune responses by the blood brain barrier, which separates nervous tissue from the peripheral circulation. Here we review evidence suggesting that an understanding of the demyelinating disorders may be helped by considering their immune pathogenesis in two stages. The first is damage to the blood brain barrier; this appears to be cell mediated, and allows infiltration into the CNS of other immune effectors. These include complement and also macrophages, which together may mediate the second stage, injury to the myelin/oligodendrocyte complex.

[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.

Relevance of platelet factor four (PF4) plasma levels in multiple sclerosis

In order to study the role of platelets in Multiple Sclerosis (MS) we assessed, in a group of patients during a quiescent phase of the disease, the plasma levels of beta-thromboglobulin (beta-TG) and platelet factor four (PF4) both in absence of treatment and during administration of aspirin (ASA) at the dose of 50 mg/daily. In the MS patients studied, the basal plasma levels of beta-TG and PF4 were significantly higher than in control subjects. The increase in the beta-TG plasma levels occurred independently of the age, sex and severity of the disease, whereas the modification in the PF4 plasma levels was significantly correlated with the severity of the disease. Administration to the patients of ASA, at the dose that does not affect prostacyclin production, determined a decrease of beta-TG in 77% of the patients. Mean PF4 plasma levels remained unchanged. These results suggest that PF4 in the plasma of MS patients may originate not only from the platelets but also from the mast cells following platelet aggregating factor (PAF) stimulation and immunocomplex formation.

Periventricular lesions in multiple sclerosis: their perivenous origin and relationship to granular ependymitis

The periventricular region was studied in the brains of 129 cases of multiple sclerosis, with the purpose of establishing the mechanism and order of events in the development of the periventricular plaque, and deciding whether there is any relationship between granular ependymitis and such plaques. Periventricular plaques were found in 82.2% of cases. Observation and computerized morphology showed that the early stage of the periventricular plaque is the formation of a lesion around a subependymal vein and that adjacent lesions later coalesce. These plaques do not appear to arise from the ependyma, which is against any role for the CSF in their initial development. Chronic or burnt-out periventricular lesions often show overlying granular ependymitis (10.9% of cases) and subependymal gliosis (17.8%), presumably as a result of the long-continued low-grade inflammatory process. This process, which is not specific for multiple sclerosis, is sometimes associated with transfer of IgG and C3, as shown with peroxidase methods, across the subependymal vein wall and the ependymal epithelium. Increased permeability of the inflamed ependyma constitutes a possible abnormal entry route from plaque to CSF or, in reverse, from CSF to brain.

Measles virus nucleic acid sequences in human brain

We constructed a measles virus genomic recombinant DNA library, and used clones coding for portions of the viral P, M and H proteins to probe for measles virus nucleic acid sequences in post-mortem multiple sclerosis, SSPE and control brains. By dot blot hybridization, the probes detected measles virus nucleic acid sequences in as little as 3 nanograms of total RNA extracted from measles virus-infected cells and also in highly diluted RNA extracted from SSPE brain, but did not detect measles virus sequences in RNA extracted from 11 multiple sclerosis or 8 control brains, even at a 1 000-fold higher concentration of RNA. By in situ hybridization, these probes detected measles virus nucleic acid sequences in virtually every cell and the surrounding neuropile of SSPE brain, but again did not detect such sequences in multiple sclerosis or control brains. Our findings using these highly specific probes confirm that measles virus is found in SSPE brains and indicate that measles virus genome is unlikely to be present in multiple sclerosis or normal brains.

The production of prostaglandin and the regulation of cell division in neonate rat primary mixed glial cultures

The production of prostaglandins has been studied in neonate rat primary mixed glial cultures. A correlation was found between inhibition of [3H]thymidine incorporation in the cultures and production of prostaglandin, which was stimulated by the addition of supernatant from Con A-activated rat splenocytes. Inhibition of prostaglandin synthesis in the cultures by indomethacin results in a striking increase in incorporation of [3H]thymidine into the cultures, an effect which was reversed by the addition of exogenous PGE2, but not PGF2 alpha. PGE was the principal prostaglandin detected, with both macrophages/microglia and astrocytes contributing to the output. A possible role for prostaglandins in the modulation of inflammatory responses in the central nervous system is discussed.

The mystery of the origin of multiple sclerosis

Our present understanding of the aetiology and pathogenesis of multiple sclerosis is discussed in relation to the views of Sir William Gowers. He perceived that both environmental and genetic factors might be implicated in the aetiology of the disease. Evidence for the former was first reported in 1903, but has become convincing only in the past 20 years; the nature of the environmental factor remains obscure. Evidence for a genetic influence on susceptibility has accumulated since the 1930s, the most compelling coming from the recent Canadian twin study. The number and mode of operation of the genetic factors is still uncertain, but there is evidence for the implication of genetically controlled cellular immune mechanisms in the pathogenesis of the disease. The precise relationship between transient changes in immunological status and the development of new lesions has yet to be defined; magnetic resonance imaging (MRI) promises to play a significant role in this analysis because of its sensitivity in detecting abnormalities in multiple sclerosis. MRI is not in itself specific; it is probable that the similar appearances in multiple sclerosis and cerebral vascular disease both derive at least in part from the influence of astrocytic gliosis on proton content and distribution. The significance of the gliosis is uncertain. Gowers believed that the primary defect in multiple sclerosis lay in the astrocyte. Recent observations on the immunological functions of this cell in vitro suggest that it could be involved early in the pathogenesis of the lesion.

Pathogenesis of multiple sclerosis. A critical reappraisal

The pathogenesis of multiple sclerosis remains a dilemma despite many years of study. Evidence for an infective agent is lacking: much doubt remains regarding the pathogenetic significance, if any, of the many reported alterations of the immune system. On the other hand, the well-documented facts that multiple sclerosis plaques are invariably located around blood vessels and that alterations of the blood-brain barrier permeability are always present in the plaque suggest that these old observations should be reconsidered. There is strong evidence to support the idea that the alteration of the blood-brain barrier is an obligatory step in the development of the plaque. It may result from a variety of environmental factors among which must be mentioned trauma to the nervous system, as well as the immunological changes resulting from viral infections and vaccinations. The available data lead to the following hypothesis: multiple sclerosis is a disease which requires the following factors for the production of demyelinating lesions of the central nervous system: a genetically determined susceptibility, an environmental, probably viral, probably immune-mediated initiatory event producing a symptomless systemic illness, a subsequent alteration of the blood-brain barrier resulting from diverse mechanisms including trauma or a second, immune-mediated event, a myelinoclastic plaque-forming mechanism which is operative only in the central nervous system.

Inflammatory vasculitis in multiple sclerosis

Fifty-two plaque or lesion areas were examined from 25 cases of multiple sclerosis. Twenty-four of these showed acute features, whereas the rest were more chronic in nature. The acute lesions showed lymphocytic infiltration (79%), fibrinous exudation (63%), lymphocytic meningitis (50%) and venulitis (58%). Of the chronic lesions, there were only 21% with lymphocytic infiltration, 11% with fibrinous exudates, none with meningitis, 29% with organising endovenulitis, 36% with fibrosed vein walls. The finding of a fibrinous inflammatory exudate in the acute lesion is a new observation in multiple sclerosis. Likewise, the observation of an inflammatory infiltrate confined to the vein wall (and often present at a distance from the plaque) has not been previously recorded in the disease. The chronic lesion, by contrast, showed relatively little fibrin, but there was considerable reparative thickening of the walls of the involved veins. The evidence provides new humoral and cellular evidence of an inflammatory process in multiple sclerosis which precedes or is not directly associated with the demyelinating process.

Multiple sclerosis: the present position

The advances of the past decade particularly in the application of evoked potential techniques and electrophoresis of CSF proteins have improved the accuracy of early diagnosis of multiple sclerosis. The geographical distribution of the disease, the effect of migration on prevalence, and the existence of clusters suggest that an environmental factor is involved in the aetiology; it is probably infective. Family and twin studies provide evidence for a genetic contribution which is probably multifactorial and related to immune regulation. The pathogenesis is at least in part immunologically mediated. A rational approach to therapy is difficult. In the present state of knowledge we are unlikely to be able to modify the course of multiple sclerosis by tackling a putative environmental agent. We are more likely to be able to do so by manipulating the pathogenesis, although an effective means of doing so has yet to be defined.

Evidence for subacute fat embolism as the cause of multiple sclerosis

The neurological features of decompression sickness, which is thought to be due to gas embolism, are similar to those of multiple sclerosis (MS). This similarity suggested the re-examination of a concept, first proposed in 1882, that the demyelination in MS is due to venous thrombosis. Unfortunately, although the plaques of MS are often perivenular, thromboses are not always present. Nevertheless, vascular theories can explain the topography of the lesions in MS. Embolism is generally associated with arterial rather than venous damage, and with neuronal infarction rather than loss of myelin. However, the intra-arterial injection of a range of substances can cause venous damage and perivenous demyelination in the brain, although it does not exactly reproduce the plaques seen in man. There is also evidence in man that fat may lodge in the microcirculation of the nervous system and cause distal perivenous oedema with the loss of myelin from axons. Since acute fat embolism may produce lesions not only in the white matter of the brain, but also in the cord, the retina, the meninges, and the skin, and since all these have been described in MS, subacute fat embolism may be the cause of MS.