Spongy degeneration of the central nervous system in infancy

Inherited and acquired disorders of myelin: The underlying myelin pathology

Remyelination is a major therapeutic goal in human myelin disorders, serving to restore function to demyelinated axons and providing neuroprotection. The target disorders that might be amenable to the promotion of this repair process are diverse and increasing in number. They range primarily from those of genetic, inflammatory to toxic origin. In order to apply remyelinating strategies to these disorders, it is essential to know whether the myelin damage results from a primary attack on myelin or the oligodendrocyte or both, and whether indeed these lead to myelin breakdown and demyelination. In some disorders, myelin sheath abnormalities are prominent but demyelination does not occur. This review explores the range of human and animal disorders where myelin pathology exists and focusses on defining the myelin changes in each and their cause, to help define whether they are targets for myelin repair therapy.

•

We reviewed myelin disorders of the CNS in humans and animals.

•

Myelin damage results from primary attack on the oligodendrocyte or myelin sheath.

•

All major categories of disease can affect CNS myelin.

•

Myelin vacuolation is common, yet does not always result in demyelination.

Alzheimer-type I astrogliopathy (AIA) and its implications for dynamic plasticity of astroglia: a historical review of the significance of AIA

Alzheimer-type I astrogliopathy (AIA) is an uncommon neuropathological phenomenon encountered in Wilson's disease and less often in acquired hepatic encephalopathy. Since its first description in 1912 it has received little attention. However, after 1971, when the nature of its morphogenesis began to be recognized and it was shown that it could be reproduced experimentally, its significance has been increasingly appreciated. Two intriguing characteristics of the dynamic plasticity of astroglia were revealed from the studies of the inter-relationships between AIA and Alzheimer-type II astrogliopathy (AIIA); normal astroglia and AIIA; and reactive astrogliosis and AIIA, namely, the compensatory "rebound" phenomenon of Alzheimer astrogliopathy, and a dual cellular origin for reactive astrogliosis taking place in both normal and dystrophic astrocytes. More recently the presence of AIA and AIIA has been reported in a case of anoxic encephalopathy, and also in a case of Marchiafava-Bignami's disease. In this review, dependable criteria for the identification of the pathological features of AIA are discussed and emphasized. Both types of Alzheimer astrogliopathy may be used as pathologic markers with specific morphological and immunocytochemical characteristics to study in detail the disturbances of metabolic interactions between the astrocyte-neuron coupling and the exact mechanisms of the dynamic plasticity of astroglia.

Spongy degeneration of white matter in the central nervous system of silver foxes (Vulpes vulpes)

A disorder of central nervous white matter in Norwegian-bred silver foxes is described from the case histories of 21 clinically affected foxes. The main presenting sign of this disorder was caudal limb ataxia, which appeared between 2 1/2 and 4 months of age and progressed over the next 4-8 weeks. Only four affected foxes were allowed to live beyond this period, but they showed moderate to marked improvement. Light microscopic examination of specimens from 16 affected foxes necropsied between 3 1/2 and 6 1/2 months of age revealed lesions that were restricted to the white matter of brain and spinal cord. The lesions were characterized by a symmetrical spongy change with vacuoles of varying sizes and included significant myelin deficiency. There was a relative preservation of axons and nerve cells and no significant inflammation or vascular reaction. An astrocytic hypertrophy was usually associated with the spongy change. Ultrastructural examination of central nervous tissue from two, perfusion-fixed, 6-month-old foxes showed intramyelin vacuoles resulting from splitting of the myelin lamellae at the intraperiod line and was interpreted as indicating myelin edema. Expanded extracellular spaces and watery astrocytic processes also contributed to the vacuolar appearance. Astrocytic processes in affected areas were hypertrophic and contained abundant filaments. Although the 16 silver foxes had severe clinical signs, their lesions had features in common with the juvenile form of Canavan's disease in children and a spongy degeneration reported in Labrador Retrievers; however, the clinical course in the foxes was not uniformly progressive.

Wilson's disease with extensive degeneration of cerebral white matter and cortex

This is a report of an autopsy case of Wilson's disease with widespread degeneration of the cerebral cortex and white matter, the basal ganglia and thalamus and, to a lesser degree, the cerebellum and brain stem. The patient was a 28-year-old man at the time of death with the clinical course of a 20-year duration. The lesions consisted of spongy degeneration leading to a cavity formation with insufficient glia fiber proliferation. We noted the characteristic findings of Alzheimer glia (Types I and II) and Opalski cells and the new formation in capillaries. The distribution of the changes in the hemispheres showed the typical pattern with a tendency of preferential superior and anterior localization and a relative preservation of the hippocampal formation, carcarine areas, amygdaloid nuclei and the hypothalamus. Similar cases in the literature were reviewed.

Dialysis encephalopathy: neuropathologic aspects

The clinical, epidemiologic, electroencephalographic, and toxicologic features of dialysis encephalopathy (DE) have been clarified, but the neuropathologic and clinicopathologic aspects of the disease have remained obscure. In three cases of DE associated with a dialysate of high aluminum content, spongy change restricted to the upper layers of the cerebral cortex was found. The spongy change was distributed through the cerebral cortex bilaterally and diffusely, but the left hemisphere was involved more severely and extensively than the right hemisphere, and the opercular portions of the frontal and temporal lobes were affected more than the remainder of those lobes. This topographic distribution correlated with the clinical defects in higher cortical functions, including aphasia. The spongy change consisted of vacuoles in the neuropil and inside nerve cell bodies. The vacuoles in the neuropil were located in dendrites, astrocytic processes, and, possibly, other structures. Thus, DE is a disease of neurons and astrocytes of the cerebral cortex. Although spongy change of the upper layers of the cerebral cortex is a nonspecific abnormality, when it occurs in the distribution described and in the absence of other diffuse cerebral diseases, it is characteristic of DE.

Neuropathology of Rett syndrome

Autopsy studies in 8 girls with the Rett syndrome dying between 4 and 15 years showed: Diffuse cerebral atrophy/micrencephaly, with a decrease in brain weight by 13.8 to 33.8% of age-matched controls, apparently related to the duration of the disorder; Mild, but inconsistent diffuse cortical atrophy without developmental disorders apart from occasional microdysgenesis (three cases), but increased amounts of neuronal lipofuscin, and occasional mild astrocytic gliosis; Mild, but inconsistent spongy changes in cerebral and cerebellar white matter, optic nerve (two cases), and myelinated fascicles of the brainstem tegmentum, without signs of dys- or demyelination, and apparently different from the spongy myelinopathy common to aminoacidopathies; Most conspicuous was an underpigmentation of the substantia nigra which contained many fewer well-pigmented neurons for age (53-73%), and fewer pigmented granules per neuron, while the total number of nigral neurons and the triphasic substructure of neuromelanin were normal for age. No pathologic changes were seen in locus coeruleus, nucleus basalis of Meynert, and nucleus dorsalis raphe; Electron microscopy of autopsy material from an 11-year-old girl showed increased amounts of neuronal lipofuscin without signs of a storage disorder. Reactive and degenerating axons in the caudate nucleus were possibly related to the nigral changes, suggesting some dysfunction of the dopaminergic nigro-striatal system, while the synaptic organization of the neostriatum appeared unaffected. Peripheral nerve from a patient dying in advanced stage showed increased numbers of unmyelinated (regenerated?) axons, with almost no demyelination and few remyelinated axons, suggesting axonal degeneration rather than hypomyelination, but exogenous factors (malnutrition) cannot be excluded. The pathogenetic mechanisms of the morphologic brain lesions and their relations to clinical and neurochemical findings in Rett syndrome are unknown and deserve further intensive investigations.

Ultrastructural findings in maple syrup urine disease in Poll Hereford calves

Ultrastructural findings in the nervous systems of two Poll Hereford calves affected with maple syrup urine disease or branched chain ketoacid decarboxylase deficiency are described. The calves were affected within 2 days of birth with a severe generalised central nervous system (CNS) disorder characterised by dullness and weakness, progressing to recumbency and opisthotonus. The urine had an odour of burnt sugar. Analysis of plasma and cerebrospinal fluid demonstrated significantly elevated levels of the branched chain amino acids leucine, isoleucine and valine. Status spongiosus affecting mainly the white matter was recorded at microscopic examination of the CNS, with ultrastructural examination confirming the presence of intramyelinic vacuole formation, suggesting myelin oedema.

Myelin oedema, optic neuropathy and retinopathy in experimental Stypandra imbricata toxicosis

Rats experimentally poisoned with the toxic plant Stypandra imbricata developed acute oedema of central and peripheral myelin and extensive axonal degeneration in the optic nerves. The oedema developed with vacuolation and splitting of myelin lamellae at the intraperiod line. Following recovery from acute intoxication, myelin oedema resolved after 6 to 12 weeks, but severe retinal degeneration and optic nerve atrophy remained. Morphological abnormalities in glial cells and axons were only found in the optic nerves. It was concluded that there is probably also a direct toxic effect on the axons of the optic nerve and the photoreceptor cells of the retina. The chemical nature of the toxin remains to be defined but the marked similarity of its toxic effects to those of hexachlorophene are noted.

Experimental spongy degeneration in calves

Experimental reproduction and ultrastructural findings of spongy degeneration of the central nervous system of hyperammonemic calves are described. Hyperammonemia was produced by intravenous infusion of ammonium acetate. Histologic findings were stereotyped in all calves and characterized by widespread vacuolation of white and grey matter of the brain spinal cord. Electron microscopy revealed widespread intramyelinic vacuoles, some expansion of extracellular spaces and swollen mitochondria. There were minimal changes in neurons, axons and glia, and little evidence of myelin breakdown. Hyperammonemia may be one of the pathogeneses involved in the CNS spongy degeneration in man and domestic animals effected with hepatocerebral diseases and some hereditary disorders.

Spongy degeneration of the central nervous system (van Bogaert-Bertrand type?) in a newborn infant. A light and electron microscopic study

Autopsy findings on a 5 day old infant with hypotonia from birth showed extensive spongy changes of the myelinating tracts within the cerebrum, cerebellum and brain stem. The spongy changes, similar to Van Bogaert-Bertrand disease, resulted from intramyelinic edema. However, unlike the typical forms of this disease, swollen astrocytes with abnormal mitochondria were not found. The relationship of this case to typical forms of Van Bogaert-Bertrand disease is discussed. This case may represent a very early form of Van Bogaert-Bertrand disease or a new pathological entity.

[Hereditary spongiform dystrophy in young children (Canavan: van Bogaert-Bertrand)]

Hereditary spongiform dystrophy in young children is characterised by macrocephaly with spasticity, convulsions and ultimately a decerebrate state and diffuse electroencephalographic changes. Histological examination of the brain remains essential for its diagnosis. A review of the ultrastructural studies reported by various authors complements the findings obtained by conventional histology. We have thus endeavoured to determine whether van Bogaert-Bertrand's disease is to be considered as congenital or acquired. The anatomical findings in 3 cases together with the descriptions of other authors lead us to the following conclusions: -that the spongiform changes may be due to an osmolar disequilibrium in which the ATPase-Na/K relation with mitochondrial abnormalities is yet unclear. -that the constant finding of Alzheimer type II cells is certainly an indication of intra-astrocytic malfunction. -that the oedema blocks both myelin synthesis and its coiling into lamellae. Case 1, which showed a long survival compared to others described (about 4 years), enabled us to study terminal lesions. Sub-cortical zones, in both cerebrum and cerebellum, contained neither myelin nor spongiform cavities, but, on the other hand, showed a compact glio-fibrillosis with large vesicles and oligodendroglia of increased density. We have interpreted these lesions, progressively replaced by spongiosis deeper in the cortex, as evidence of retracted scar tissue. Differences found between cerebral weights seem to confirm this hypothesis.

Infantile spongy degeneration of the central nervous system associated with glycogen storage and markedly fatty liver

The clinical, biochemical, and pathological features of an unusual expression of infantile spongy degeneration of the central white matter are presented with emphasis on neuropathological observations. The topographical distribution of the spongy change along with the observed defect in myelination were such as to suggest an arrest in development of the white matter in late foetal life. Of additional interest, in the present case, is the observed deposition of glycogen in the brain, heart, and liver along with a markedly fatty liver. Our findings are compared with those in other cases of so-called spongy degeneration, as well as with certain of the aminoacidurias and, as a consequence, we wish to suggest that the basic pathogenetic factor probably lies in a disturbance of the biochemical energy supply system rather than in a disorder of myelin lipid metabolism per se.