Online newspaper of professor Yasser Metwally

It is quite apparent that postinfectious neurological disorders have protean clinical presentations depending upon the site(s) involved in the central or peripheral nervous system. Postinfectious neurological disorders might involve the brain and spinal cord (postinfectious encephalomyelitis), the cerebellar only (postinfectious cerebellitis), The spinal cord only (postinfectious acute idiopathic transverse myelitis), The optic nerve only (optic neuritis in children) or the optic nerve and spinal cord (neuromyelitis optica). It is not known whether these disorders represent a single disease with different clinical presentations or different diseases. Pathologically spinal cord involvement in neuromyelitis optica and acute disseminated encephalomyelitis is a transverse myelitic process identical to that of isolated acute idiopathic postinfectious transverse myelitis. Bilateral optic neuritis is characteristically present in acute disseminated encephalomyelitis. It looks like that the division between these postinfectious demyelinating disorders is indistinct, which is suggestive of a clinical continuum.

Benign regressive postinfectious neurological disorders (BRPIND) comprises a group of poorly understood inflammatory/demyelinating white matter disorders of cerebrum, cerebellum and spinal cord that is characteristically postinfectious in nature. It is unclear what are the triggers and effector mechanisms resulting in white matter insult, though tantalizing clues have emerged. These disorders exist on a continuum of postinfectious neuroinflammatory and white matter demyelinative background that includes Guillain-Barre syndrome (GBS), acute disseminated encephalomyelitis (ADEM), Neuromyelitis Optica (NMO), optic neuritis, transverse myelitis and postinfectious cerebellitis. Each of these disorders differs in the spatial and temporal restriction of inflammation within the nervous system. However, clinical and pathologic studies support the notion that there are many common features of the inflammation and white matter demyelination that is postinfectious or postvaccinal in nature.

The disease is better termed cerebral ADEM (Acute disseminated encephalitis), Spinal ADEM (acute postinfectious transverse myelitis), Cerebellar ADEM (acute postinfectious cerebellitis), Optic ADEM (Optic neuritis in children)…etc. ADEM is probably the clinico-pathological category under which all other subtypes are filed. 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 postinfectious transverse myelitis), The cerebellum only (acute postinfectious cerebellitis), The optic nerves and the spinal cord (neuromyelitis optic), or the optic nerves only (optic neuritis in children) [1]. Other terminologies might even be suggested like ataxic ADEM (acute postinfectious cerebellitis), myelitic ADEM (acute postinfectious 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 postinfectious 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 postinfectious disorders is 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 end 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. [1]

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. In particular postinfectious isolated transverse myelitis is the most common clinical presentation of this disorder in the author experience, probably this signifies the selective involvement of the descending corticospinal and pyramidal tract fibers.

Myelin destruction and inflammatory white matter demyelination is an immune-mediated mechanism in Benign regressive postinfectious neurological disorders (BRPIND) 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. The description of these immune mediated mechanisms are beyond the scope of This chapter. [1]

Benign regressive postinfectious neurological disorders (BRPIND) most commonly occur after smallpox and measles infections. In recent years, the disease has been associated with various viral and bacterial infections. Patients may have a history of an exanthem or a nonspecific respiratory or gastrointestinal illness 1 to 3 weeks before onset of neurologic symptoms. Acute cerebellar ataxia is a form of acute postinfectious encephalomyelitis following varicella infection. [1]

Post-immunization BRPIND occur most frequently following measles, rubella, or mumps vaccination. Many vaccines have been implicated in the causation of BRPIND [Table - 1]. In countries where neural tissue-based vaccines are still used, antirabies immunization with either BPL (betapropionolactone inactivated) or Semple (phenol inactivated) vaccines are important causes for BRPIND. [1]

Table 1. Infections alleged to cause BRPIND ^[1]

References

1. Metwally, MYM: Textbook of neuroimaging, A CD-ROM publication, (Metwally, MYM editor) WEB-CD agency for electronic publication, version 10.1a January 2009 [Click to have a look at the home page]