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Keeping it simple: is there a need for the various subtyping of axonal forms of Guillain–Barré syndrome?
  1. Nobuhiro Yuki1,
  2. Nortina Shahrizaila2
  1. 1Departments of Microbiology and Medicine, National University of Singapore, Singapore
  2. 2Division of Neurology, Department of Medicine, University of Malaya, Kuala Lumpur, Malaysia
  1. Correspondence to Professor N Yuki, Department of Microbiology, National University of Singapore, 5 Science Drive 2, Blk MD4A, Level 5, Singapore 117597, Singapore; micyuki{at}nus.edu.sg

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Guillain–Barré syndrome (GBS) can be classified into demyelinating and axonal forms based on the underlying pathogenesis. The axonal form of GBS was further classified into two subtypes, acute motor axonal neuropathy (AMAN) and acute motor and sensory axonal neuropathy (AMSAN).1 Capasso et al2 have elegantly demonstrated that sensory fibres are often subclinically involved in AMAN through serial sensory nerve conduction studies (see page 664). They have also shown that reversible conduction failure occurs in sensory as well as motor fibres in AMAN and AMSAN. The authors concluded that both subtypes form a continuous spectrum.

The pathology of AMAN and AMSAN are similar, and both conditions can be preceded by Campylobacter jejuni enteritis.1 The difference between the two subtypes is the involvement of both the dorsal and ventral roots in AMSAN compared with just the ventral roots in AMAN. IgG anti-GM1 and anti-GD1a antibodies are immunological markers that differentiate AMAN from acute inflammatory demyelinating polyneuropathy, and patients with AMAN and AMSAN also share these serological markers.3 This common immunological profile supports the notion that AMAN and AMSAN are in fact the result of a single immune response against the axon rather than two separate disease entities. The pathological findings suggest that AMSAN is a more extensive form of the AMAN spectrum.1

Bovine brain ganglioside mixture consists of GM1 and GD1a. Reports of patients developing AMAN following the administration of bovine brain ganglioside mixture or isolated GM1 have been recorded, and these patients were found to have IgG anti-GM1 or anti-GD1a antibodies. The animal model of AMAN was developed by inoculating rabbits with the ganglioside mixture, GM1 or GM1-like lipo-oligosacchaide of C jejuni.4 The pathological features of these rabbits were consistent with those of human AMAN, exhibiting Wallerian-like degeneration, but neither demyelination nor T cell infiltration were seen in the motor nerves. The acute progressive phase of AMAN rabbits shows IgG and complement being deposited at the nodes of Ranvier in the anterior spinal roots and membrane attack complex formation at the nodal axolemma. Thereafter, voltage gated sodium channels disappear and paranodal myelin terminal loops are detached. These pathological changes could account for the reversible conduction block sometimes seen in milder forms of AMAN and the subsequent axonal degeneration producing muscle weakness in severe AMAN cases.

Acute motor conduction block neuropathy (AMCBN) has also been proposed as an axonal variant of GBS.5 There is typically a history of diarrhoea with evidence of C jejuni infection and IgG anti-GM1 antibodies. Some AMAN patients had reversible conduction block in the forearm segment, similar to that seen in AMCBN, whereas others had conduction block followed by axonal degeneration.6 These observations suggest that AMCBN is a less extensive form of AMAN, characterised by reversible conduction block in the motor nerves.

At present, there are various proposed subtypes of axonal GBS, such as AMCBN, AMAN and AMSAN, which are based on serial electrophysiological findings. However, these subtypes are part of the same disease spectrum and differ mainly in terms of their disease extent and severity. We would suggest that GBS be simply classified electrophysiologically into acute inflammatory demyelinating polyneuropathy and AMAN. In the ‘AMAN’ subtype, serial electrophysiology may be utilised to further subtype AMCBN, classical AMAN and AMSAN within this AMAN spectrum. This approach may help to prognosticate the disease in terms of its extent.

References

Footnotes

  • Linked article 238311.

  • Competing interests None.

  • Provenance and peer review Commissioned; not externally peer reviewed.

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