Central pontine myelinolysis. An ultrastructural and elemental study

Central pontine myelinolysis and the osmotic demyelination syndromes: an open and shut case?

Central pontine myelinolysis and extrapontine myelinolysis are collectively called the osmotic demyelination syndromes. Despite being described in 1959, there are several aspects of the disorder that remain an enigma. Animal models and neuroimaging techniques have allowed us to understand the condition better. From being a universally fatal disorder that was diagnosed post mortem, increased awareness, neuroimaging techniques and supportive care have enabled us to make the diagnosis ante-mortem. This has also led to a significant drop in associated mortality. The aim of this review is to highlight the clinical spectrum, neuroimaging findings, and recent developments.

Human alcohol-related neuropathology

Alcohol-related diseases of the nervous system are caused by excessive exposures to alcohol, with or without co-existing nutritional or vitamin deficiencies. Toxic and metabolic effects of alcohol (ethanol) vary with brain region, age/developmental stage, dose, and duration of exposures. In the mature brain, heavy chronic or binge alcohol exposures can cause severe debilitating diseases of the central and peripheral nervous systems, and skeletal muscle. Most commonly, long-standing heavy alcohol abuse leads to disproportionate loss of cerebral white matter and impairments in executive function. The cerebellum (especially the vermis), cortical-limbic circuits, skeletal muscle, and peripheral nerves are also important targets of chronic alcohol-related metabolic injury and degeneration. Although all cell types within the nervous system are vulnerable to the toxic, metabolic, and degenerative effects of alcohol, astrocytes, oligodendrocytes, and synaptic terminals are major targets, accounting for the white matter atrophy, neural inflammation and toxicity, and impairments in synaptogenesis. Besides chronic degenerative neuropathology, alcoholics are predisposed to develop severe potentially life-threatening acute or subacute symmetrical hemorrhagic injury in the diencephalon and brainstem due to thiamine deficiency, which exerts toxic/metabolic effects on glia, myelin, and the microvasculature. Alcohol also has devastating neurotoxic and teratogenic effects on the developing brain in association with fetal alcohol spectrum disorder/fetal alcohol syndrome. Alcohol impairs function of neurons and glia, disrupting a broad array of functions including neuronal survival, cell migration, and glial cell (astrocytes and oligodendrocytes) differentiation. Further progress is needed to better understand the pathophysiology of this exposure-related constellation of nervous system diseases and better correlate the underlying pathology with in vivo imaging and biochemical lesions.

Human alcohol-related neuropathology

Alcohol-related diseases of the nervous system are caused by excessive exposures to alcohol, with or without co-existing nutritional or vitamin deficiencies. Toxic and metabolic effects of alcohol (ethanol) vary with brain region, age/developmental stage, dose, and duration of exposures. In the mature brain, heavy chronic or binge alcohol exposures can cause severe debilitating diseases of the central and peripheral nervous systems, and skeletal muscle. Most commonly, long-standing heavy alcohol abuse leads to disproportionate loss of cerebral white matter and impairments in executive function. The cerebellum (especially the vermis), cortical-limbic circuits, skeletal muscle, and peripheral nerves are also important targets of chronic alcohol-related metabolic injury and degeneration. Although all cell types within the nervous system are vulnerable to the toxic, metabolic, and degenerative effects of alcohol, astrocytes, oligodendrocytes, and synaptic terminals are major targets, accounting for the white matter atrophy, neural inflammation and toxicity, and impairments in synaptogenesis. Besides chronic degenerative neuropathology, alcoholics are predisposed to develop severe potentially life-threatening acute or subacute symmetrical hemorrhagic injury in the diencephalon and brainstem due to thiamine deficiency, which exerts toxic/metabolic effects on glia, myelin, and the microvasculature. Alcohol also has devastating neurotoxic and teratogenic effects on the developing brain in association with fetal alcohol spectrum disorder/fetal alcohol syndrome. Alcohol impairs function of neurons and glia, disrupting a broad array of functions including neuronal survival, cell migration, and glial cell (astrocytes and oligodendrocytes) differentiation. Further progress is needed to better understand the pathophysiology of this exposure-related constellation of nervous system diseases and better correlate the underlying pathology with in vivo imaging and biochemical lesions.

Evidence of aquaporin involvement in human central pontine myelinolysis

BACKGROUND

Central pontine myelinolysis (CPM) is a demyelinating disorder of the central basis pontis that is often associated with osmotic stress. The aquaporin water channels (AQPs) have been pathogenically implicated because serum osmolarity changes redistribute water and osmolytes among various central nervous system compartments.

RESULTS

We characterized the immunoreactivity of aquaporin-1 and aquaporin-4 (AQP1 and AQP4) and associated neuropathology in microscopic transverse sections from archival autopsied pontine tissue from 6 patients with pathologically confirmed CPM. Loss of both AQP1 and AQP4 was evident within demyelinating lesions in four of the six cases, despite the presence of glial fibrillary acidic protein (GFAP)-positive astrocytes. Lesional astrocytes were small, and exhibited fewer and shorter processes than perilesional astrocytes. In two of the six cases, astrocytes within demyelinating lesions exhibited increased AQP1 and AQP4 immunoreactivities, and gemistocytes and mitotic astrocytes were numerous. Blinded review of medical records revealed that all four cases lacking lesional AQP1 and AQP4 immunoreactivities were male, whereas the two cases with enhanced lesional AQP1 and AQP4 immunoreactivities were female.

CONCLUSIONS

This report is the first to establish astrocytic AQP loss in a subset of human CPM cases and suggests AQP1 and AQP4 may be involved in the pathogenesis of CPM. Further studies are required to determine whether the loss of AQP1 and AQP4 is restricted to male CPM patients, or rather may be a feature associated with specific underlying precipitants of CPM that may be more common among men. Non-rodent experimental models are needed to better clarify the complex and dynamic mechanisms involved in the regulation of AQPs in CPM, in order to determine whether it occurs secondary to the destructive disease process, or represents a compensatory mechanism protecting the astrocyte against apoptosis.

Neuromyelitis optica: a demyelinating disease characterized by acute destruction and regeneration of perivascular astrocytes

BACKGROUND

A serum antibody directed against astrocytes is present in a high proportion of patients with neuromyelitis optica (NMO). The pathogenicity of the antibody is uncertain because no consistent astrocyte lesion is known to occur in NMO.

OBJECTIVE

To determine whether there is an astrocyte lesion in NMO and if this differs from astrocyte changes in multiple sclerosis (MS).

METHODS

Astrocyte pathology in early (still-myelinated) lesions and subacute NMO and MS lesions was examined immunohistochemically and in sections stained for astrocytes using routine histological techniques.

RESULTS

Demyelination in early NMO lesions is accompanied by oligodendrocyte apoptosis in a pattern identical to that seen in MS and this is preceded by an abrupt destruction of perivascular astrocytes. Reparative astrogliosis is effected by a population of unipolar, new astrocytes. Evidence of a different type of astrocyte lesion was found in MS.

DISCUSSION

The findings add to experimental evidence that the antibody is pathogenic. They also raise the possibility that demyelination in MS may be a bystander effect of an astrocyte lesion, i.e. that MS is not a disease primarily of myelin and oligodendrocytes.

Central pontine myelinolysis: historical and mechanistic considerations

Central pontine myelinolysis (CPM) is a demyelinating condition affecting not only the pontine base, but also involving other brain areas. It usually occurs on a background of chronic systemic illness, and is commonly observed in individuals with alcoholism, malnutrition and liver disease. Studies carried out 25-30 years ago established that the principal etiological factor was the rapid correction of hyponatremia resulting in osmotic stress. This article reviews progress achieved since that time on its pathogenesis, focusing on the role of organic osmolytes, the blood-brain, barrier, endothelial cells, myelinotoxic factors triggered by osmotic stress, and the role of various factors that predispose to the development of CPM. These advances show great promise in providing novel therapeutic options for the management of patients afflicted with CPM.

Immunoglobulins are effective in pontine myelinolysis

Although the exact pathogenesis of central pontine myelinolysis (CPM) is unknown, correction of hyponatremia, thyreotropin releasing hormone, plasmapheresis, and corticosteroids seem to be effective. Assuming intravenous immunoglobulins (IVIG) to also be effective in CPM, 0.4 g/kg body weight/d immunoglobulins were applied to a 48-year-old patient who developed CPM with double vision, dysarthria, dysphagia, and left-sided hemiparesis 3 weeks after spontaneous normalization of hyponatremia. After 5 days of IVIG, his symptoms markedly improved, confirmed by improvement in the Norris score (42%), Frenchay score (19%), Kurtzke score (20%), Disability score (54%), vital capacity (26%), and peak torque (69%). The promising clinical effect of IVIG was assumed to be caused by the reduction of myelinotoxic substances, the development of antimyelin antibodies, and the promotion of remyelination. In conclusion, IVIG appear to be a promising therapeutic option in CPM.

Electrolyte-induced demyelination in rats. 2. Ultrastructural evolution

This study presents the electron microscopic evolution of lesions in electrolyte-induced demyelination (EID) in rats, a lesion which bears striking histological and clinical similarity to central pontine myelinolysis. The earliest change was observed during the hyponatremic phase and consisted of minimal intracellular edema present throughout the brain. Following the injection of hypertonic saline, additional changes were observed which were restricted to sites previously reported to be frequently involved in EID. Early dilatation of the inner tongue of oligodendrocyte cytoplasm in myelinated nerve fibers was observed at 3 h post hypertonic saline injection (PHS). This was followed, at 48 h PHS, by the appearance of degenerative changes consistent with dying oligodendrocytes. Well-delineated, vacuolar and spongy lesions, seen by light microscopy, were present by 48 h PHS at the same sites as above. Electron microscopically, this appearance was found to be due to striking intramyelinic edema. By 96 h PHS, macrophages containing myelin and other cellular debris were frequently present at these sites. Concomitantly, myelin sheaths underwent vesicular disruption and disintegration. This sequence of events suggests a lesion of the oligodendrocyte-myelin complex, secondary to initial blood-brain barrier damage and edema.

Electrolyte-induced demyelination in rats. 1. Role of the blood-brain barrier and edema

The blood-brain barrier (BBB) was studied in rats with electrolyte-induced demyelination (EID), an experimental model for central pontine myelinolysis. Intravenously injected peroxidase was extravasated at 3 h post hypertonic saline injection (PHS) into regions frequently involved in EID. Increased pinocytotic activity and focal interendothelial gaps were seen at 3 h PHS and less frequently at 48 h PHS. Measurement of total cerebral water content revealed an increase during the hyponatremic phase. This was followed by a marked increase at 3 h PHS with continued increment at 48 h PHS. Intracellular edema with accumulation of fluid within neurites and astrocytic processes was noted during the hyponatremic phase, whereas extracellular edema developed after hypertonic saline injection. The implications of disrupted BBB and its role in the pathogenesis of EID are discussed.

Neuropathologic findings after liver transplantation

Neuropathologic findings are described in 37 patients autopsied after one or more orthotopic liver transplants. Gross or microscopic lesions were observed in almost all patients, including anoxic-ischemic change, hemorrhages and/or infarcts, and opportunistic infections by fungi (most commonly Aspergillus) and rarely viruses (cytomegalovirus). Central pontine and extra-pontine myelinolysis was commonly observed, and appeared to result from severe multifactorial metabolic abnormalities in the perioperative period. Low-grade (microglial nodule) encephalitis without an obvious pathogen was often encountered. Common clinical neurologic abnormalities included encephalopathy, seizures (myoclonic, focal or generalized), obtundation and coma. These were found more commonly than focal findings, but clinical features in a given patient were not uniformly predictive of underlying neuropathologic change.

Changes in glial cell markers in recent and old demyelinated lesions in central pontine myelinolysis

An immunohistochemical study was performed to compare glial reactions in recent and old lesions of central pontine myelinolysis (CPM). Regions of demyelination and destruction of oligodendrocytes, showed reduced immunoreactivity of myelin basic protein (MBP), myelin-associated glycoprotein (MAG), transferrin, and carbonic anhydrase C (CA C). In addition, labeling of glial fibrillary acidic protein (GFAP) and S-100 protein revealed distinct dystrophic alterations of the astroglia. Remarkably, immunolabeling of GFAP was drastically reduced in astrocytic cytoplasm within freshly demyelinated lesions. Immunostaining of vimentin revealed a differential intracytoplasmic decoration of hypertrophic and dystrophic astrocytes in recent and old CPM lesions. Immunolabeling of desmin failed to stain glial cells. Monoclonal antibodies against HNK-1 exhibited greatly increased immunoreactivity both of persisting oligodendrocytes and of reactive fibrillary astrocytes in old CPM foci. In freshly demyelinated lesions, enhanced immunoreactivity of the X-hapten (3-fucosyl-N-acetyllactosamine) was prominent in astroglia and oligodendrocytes. Simultaneously, reactive astrocytes revealed intracytoplasmic labeling of laminin. Quantitation of GFAP+ astroglia in fresh CPM and control cases revealed an increase in the number of astrocytes within the demyelinated foci and in the surrounding non-demyelinated pontine tissue of CPM cases. The occurrence of astroglial alterations in the demyelinated foci of CPM could be interpreted as "astroglial dystrophy" which may represent a pathogenic factor in CPM. Furthermore, it is possible that changes of the glial microenvironment may influence the astroglia to revert transiently back to an immature phenotype as indicated by the enhanced expression of the X-hapten and HNK-1, and the de novo synthesis of vimentin and laminin.

[Central pontine myelosis. Morphology and forensic importance]

Central pontine myelinolysis (CPM) evidently occurs more frequently than had been assumed up to now owing to the cases that have been substantiated solely on the basis of pathological anatomy. Its genesis is still unclarified. Computed tomography and magnetic resonance methods allow detection of the foci while the affected person is still alive. They are clearly capable of regression and are not automatically accompanied by a poor prognosis. Since an iatrogenic factor (forced compensation of hyponatremia) is increasingly under discussion as the cause of CPM, the condition also has substantial significance from a forensic point of view. On the basis of a prospective study on CPM confirmed in 100 brains of alcoholics, as well as 4 further cases from the forensic autopsy material, it is shown that hyponatremia is not likely to be the sole triggering factor. The course of the condition in the cases investigated shows that the capacity for action may be preserved up to death (which has occurred for other reasons) in not very pronounced CPM. In questionable violent and other unclear deaths, CPM must also be considered a possible cause of death. The various hypotheses on its etiology in the extensive literature are compared with the findings in our own cases and discussed.

[Central pontine and extrapontine myelinolysis: report of an autopsied case and review of the literature]

An autopsied case of central pontine and extrapontine myelinolysis in a 16-year-old diabetic girl is described. Due to dehydration she was treated vigorously with daily intravenous isotonic saline, from the first day of hospitalization. In the first three days the serum sodium level increased by more than 30 mEq/l when compared with the initial level. By the next days the serum sodium level, after a mild drop, rose again and was maintained above normal range for a further 12 days. On the sixth day of this new and sustained serum sodium increase, the patient presented progressive neurological manifestations that remained until her death, characterized by mutism, inability to eat, to move her head, trunk, and members and, in addition, retention of respiratory secretions. The neuropathological examination showed massive central pontine myelinolysis and similar myelinolytic lesions in the subcortical white matter of the temporal lobe, the right optic tract, the external and extreme capsules to the right, the main mammillary tract and the subcortical white matter of the left cerebellar hemisphere. The review of the literature on central pontine and extrapontine myelinolysis shows that the present case is the 30th of such condition. The clinical picture and the etiopathogenesis of central pontine and extrapontine myelinolysis are commented upon. It is suggested, as possible causative factors, the persistent and rapid correction of serum sodium concentration as well as its fluctuation in patients with hyponatremia and/or dehydration.

Central pontine myelinolysis: diagnosis by computed tomography, magnetic resonance and evoked potentials

The intravital diagnosis of central pontine myelinolysis has become possible with the introduction of computed tomography and magnetic resonance into neurological diagnostics. These tools are of special value when neurological signs of a ventral pontine lesion are lacking, as in the case we describe. Auditory evoked potentials likewise confirm their diagnostic value with regard both to the site of the lesion and to its dorsal extent toward the pontine tegmentum.

Hyponatremia: cerebral symptoms and role in central pontine myelinolysis

Central nervous system symptoms due to hyponatremia is highly dependent on its acuteness and cause. Severe acute hyponatremia (serum sodium less than 125 mEq/l) often causes confusion, lethargy, seizures or frank coma due to brain oedema. If therapy is delayed, hyponatremia carries a high mortality rate, and risk of irreversible brain damage. Hyponatremia should probably be corrected to 125-130 mEq/l at a rate of 1.5-2.0 mEq/l/h. Malnourished alcoholic patients with hyponatremia may represent a special case with possible dangers of central pontine myelinolysis if a very low serum sodium is corrected acutely to normonatremic or hypernatremic levels. Mortality in this subgroup is high whatever the therapy.

Alcoholic brain damage and neurological symptoms of alcohol withdrawal--manifestations of overhydration

Central nervous system damage is a major complication of alcohol abuse. Vitamin deficiency, particularly thiamine deficiency, has a role in producing pathological and psychological changes of alcoholic brain damage, but it is likely that alcohol has a direct toxic effect on the brain. It is proposed that neuropathological abnormalities seen in alcoholics, and also neurological symptoms during alcohol withdrawal, may reflect cerebral edema caused by alcohol. The neurological symptoms of alcohol withdrawal show a similarity to those seen in hyponatremia or water intoxication. It is suggested that alcoholics show overhydration particularly during withdrawal and that pathological changes in the alcoholic brain are related to cerebral edema. Cerebral edema in withdrawing alcoholics may be caused by inappropriate section of vasopressin (antidiuretic hormone).

Central pontine myelinolysis following rapid correction of hyponatremia

Central pontine and extrapontine myelinolysis was experimentally produced in dogs by the rapid correction of severe, sustained, vasopressin-induced hyponatremia. Hyponatremia alone or slowly corrected hyponatremia did not produce the disease. Affected dogs showed rigid quadriparesis. The central pons, lateral aspects of the thalamus and adjacent internal capsules, deep layers of cerebral cortex and subjacent white matter, cerebellum, and other regions were symmetrically involved. Myelin and oligodendroglia were affected out of proportion to axons and neurons. Thus, the clinical features, the distribution of the lesions, and their histological features closely resemble the human disease. These experiments document an electrolyte manipulation that can cause permanent neuropathological lesions. Taken with the available clinical data on human patients, the experimental results indicate that human myelinolysis may be due to a rapid increase in serum sodium from previously low levels, and that rapid normalization of severe, sustained hyponatremia should therefore be avoided.

Association between rise in serum sodium and central pontine myelinolysis

Twelve hyponatremic patients with central pontine myelinolysis (CPM) showed a rise in serum sodium levels 3 to 10 days (mean, 6) prior to the development of CPM. The increase exceeded 20 mEq/L within 1 to 3 days and was then sustained for an additional 3 to 5 days. In addition, 11 of the 12 CPM patients achieved a sodium value of 147 mEq/L or greater during the period of sodium elevation. The rise in sodium frequently coincided with administration of saline solutions, diuretics, steroids, and lactulose. In contrast, 9 hyponatremic patients who did not have CPM showed sodium increases that were significantly less or slower (or both) following treatment of hyponatremia. Our findings suggest that CPM may be caused by a too rapid or excessive rise in serum sodium from a hyponatremic baseline.

Central pontine myelinolysis in association with Hodgkin's lymphoma

Central pontine myelinolysis was found histologically in a young man who died with Hodgkin's lymphoma. Clinically he had developed a progressive peripheral sensory deficit, ataxia, quadriparesis, dysarthria, incontinence and drowsiness. This is the fifth case reported in the British literature. The pathogenesis and aetiology of this primary demyelinating disease are considered.

Rapid correction of hyponatremia causes demyelination: relation to central pontine myelinolysis

The human demyelinative disorder central pontine myelinolysis may be an iatrogenic disease caused by a rapid rise in serum sodium, usually when hyponatremia is corrected. Rats treated with hypertonic saline after 3 days of vasopressin-induced hyponatremia had demyelinative lesions in the corpus striatum, lateral hemispheric white matter, cerebral cortex, hippocampal fimbria, anterior commissure, thalamus, brainstem tegmentum, and cerebellum. Thus, rapid correction of hyponatremia can lead to demyelinative lesions and may be the cause of central pontine myelinolysis in man.

Central pontine myelinolysis

This appears to be the first report of a case of central pontine myelinolysis associated with chronic alcoholism and liver cirrhosis in the United Kingdom. The pathological features and theories of aetiology are briefly discussed.

Demyelination of the lateral geniculate nucleus in central pontine myelinolysis

Postmortem examination of the central nervous system in 6 of 9 patients with central pontine myelinolysis (CPM) revealed demyelination in the lateral geniculate nucleus (LGN). Histologically, the geniculate lesions consisted of myelin swelling and disintegration, largely in the central part of the nucleus, with preservation of axons and neuronal perikarya. The pathological changes resembled those found in the basis pontis in CPM.

Auditory evoked responses and computerized tomography in central pontine myelinolysis

We present the first case of central pontine myelinolysis (CPM) confirmed by high resolution computerized tomography (CT) in which auditory brainstem responses (ABR) revealed impaired conduction beyond the mid pons. The combined use of CT and ABR in the diagnosis of central pontine myelinolysis is discussed.

Hereditary myelopathy of Afghan hounds, a myelinolytic disease

A disease described previously as hereditary necrotizing myelopathy and myelomalacia was studied in four Afghan hounds. Light and electron microscopic investigation revealed sieve-like degeneration of spinal white matter. Despite extensive spongiform degeneration of myelin that progressed to micro- and macro-cavitation, substantial numbers of axons were preserved. This canine myelopathy was compared and contrasted with various toxic/metabolic conditions including subacute combined degeneration.

Immunofluorescence studies of intra cytoplasmic immunoglobulin binding lymphoid cells (CILC) in the central nervous system. Report of 32 cases including 19 multiple sclerosis

In 32 cases of human neurological disorders, including 19 cases of Multiple Sclerosis, an analysis was performed on formalin fixed paraffin embedded brain tissue by using fluorescein labelled antibodies and Nomarski optics. This method, which allows the reduction of technical artifarcts, permitted to establish the presence of intracytoplasmic immunoglobulin binding lymphoid cells with IgG and IgA, more rarely IgM, in the majority of the multiple sclerosis cases. This supports the theory of the intrathecal secretion of antibodies within the central nervous system but does not allow to explain the function of those B. Lymphocytes. The same immunological picture was found in Subacute Sclerosing Panencephalitis. On the contrary, it was different in Progressive Multifocal Leucoencephalopathy.