The Demyelinating Diseases and Recent Advances

The term ' demyelinating diseases' is applied to a group of disorders of the central nervous system which show loss of the normal myelination of the white matter and in which this loss is regarded as being of especial importance. This paper is a short review of such conditions and it will also include a brief survey of recent research work which it is believed may throw light on them, particularly with regard to aetiology and pathogenesis. Loss of the myelin in the white matter of the brain or spinal cord frequently can be recognized by the naked eye, but it may require demonstration by special histological methods based upon specific staining of myelin and its absence in areas of demyelination. In addition, special histological techniques are employed to show the presence of abnormal substances, some derived from breaking down myelin, in the pathological areas. Apart from such changes there may be reactions in the mesodermal elements and abnormal accumulations of cells derived from the blood, as well as hypertrophy and proliferation of the astrocytic cells and fibres giving rise to the sclerotic changes seen in some of the subacute and chronic diseases. Numerous conditions may cause loss of myelin, such as infarction and cerebral softening, invasion or compression by neoplasms, Wallerian degeneration due to loss or damage of the neurones or their processes, and ascending or descending tract degeneration. Strich (I955) has described an extensive degeneration of the cerebral white matter following head injuries. However, these conditions are not usually included in the group of diseases under discussion. An attempt will be made to provide a classification of the demyelinating diseases, but it should be remembered that there is much overlapping between the different types described. However, such a classification may be of value in identifying or labelling a particular case. Clinically