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Abstract
Post infectious demyelinating neurological disorders are a group of neurological disorders that are characteristically post infectious, post vaccination in nature; they are a white matter demyelinating monophasic pathological process that has a regressive, benign and self-limiting course.
ADEM is a collective pathological terminology that can involve the cerebrum only (Acute disseminated encephalitis or much better termed acute disseminated cerebritis), the spinal cord only (acute post infectious transverse myelitis), The cerebellum only (acute post infectious cerebellitis), The optic nerves and the spinal cord (neuromyelitis optic), or the optic nerves only (optic neuritis in children) . Other terminologies might even be suggested like ataxic ADEM (acute post infectious cerebellitis), myelitis ADEM (acute post infectious transverse myelitis)...etc. Predominantly brainstem presentation with features suggesting Miller-Fisher syndrome might occasionally be encountered (? brain stem ADEM). Miller-Fisher syndrome can occasionally be post infectious in nature.
These disorders might coexist in various combinations in the same patient or might present clinically as an isolated disease. It looks like that the division between these post infectious disorders are indistinct, which is suggestive of a clinical continuum. These disorders simply represent a single disease with different clinical presentations.
Myelin basic protein (which is the main antigen that is targeted in the immune mechanism that ends in myelin destruction) is different in different parts of the CNS. The myelin basic protein in the peripheral nerves is different from that of the CNS and this might explain why the demyelinative process may preferentially involves some parts of the CNS and spare other parts in different patients (depending upon the antigenic properties of the myelin basic protein of the involved sites) resulting in a protean clinical presentations of the same disease in different patients.
Different areas of the white matter within the CNS and the peripheral nervous system are targeted by the inflammatory demyelinating pathological process in various combinations in different patients depending upon the antigenic properties of the myelin basic protein in these areas resulting in some patients having their optic nerves, cerebrum, and spinal cord involved (acute disseminated encephalomyelitis), other patients having their optic nerves and spinal cord involved (neuromyelitis optica) and so on.
Although almost any portion of the CNS may be clinically involved, certain systems appear to be particularly prone to dysfunction; thus, the descending white matter motor tracts (the corticospinal tract, pyramidal tract), optic nerves, and spinal cord are particularly commonly involved.
Myelin destruction and inflammatory white matter demyelination is an immune-mediated mechanism in post infectious demyelinating neurological disorders that is triggered by antecedent infection. The immune mechanisms include antibody-mediated complement dependant myelinolysis, T-cell mediated lysis of Schwann cells and T -cell mediated induction of an immune reaction with release of cytokines and recruitment of inflammatory cells including macrophages