Acute Motor Axonal Neuropathy

Original Editor - Jonathan Wong Top Contributors - Jonathan Wong, Carina Therese Magtibay, Rucha Gadgil, Kim Jackson and Khloud Shreif

Introduction[edit | edit source]

Acute motor axonal neuropathy (AMAN) is classified as a subtype of Guillain–Barré syndrome (GBS)[1]. The disease was first discovered in China and was nicknamed 'chinese paralytic disease'[1]. Pathology in AMAN patients are usually limited to the motor nerve, with macrophages destroying axons while myelin remains intact, a contrast to AIDP GBS (most common form of GBS) which is known as a demyelinating disease[1]. While AMAN mainly involves axonal damage to motor nerve fibres; acute inflammatory demyelinating polyradiculoneuropathy (AIDP) involves both motor and sensory nerve fibre damage due to demyelination[1].

AMAN has an estimated prevalence of 30–65% in Asia, Central and South America[2].

Aetiology[edit | edit source]

  • AMAN is strongly linked to Campylobacter jejuni and Zika virus infection.[3][4]
  • AMAN has some documented association with hepatitis E infection.[5]

Pathogenesis[edit | edit source]

GBS is a post-infectious disorder with two-thirds of patients presenting symptoms of a respiratory or gastrointestinal tract infection before the onset of GBS[6].

Serum antibodies against GM1a, GM1b, GD1a and GalNAc-GD1a gangliosides are noticeable in patients with AMAN[6]. Studies have also shown complement activation causing nerve degeneration at the nodes of Ranvier and at the motor nerve terminal in a mouse model of AMAN.[7]

Clinical features[edit | edit source]

AMAN presents similarly in terms of clinical features as well as CSF findings to GBS:[1]

  • Weakness of limbs (earliest symptom is weakness of lower limbs)
  • Weakness of respiratory muscles
  • Gradual weakening and finally, absence of tendon reflexes
  • Bulbar palsy in 61% of patients[1]
  • Autonomic dysfunction and pain[8]

However, it generally presents without any sensory symptoms, unlike AIDP-GBS[5], although it can present with sensory symptoms[9]. A neurophysiological screen in patients with AMAN should also show no evidence of demyelination, unlike GBS[5].

Differential Diagnosis[edit | edit source]

The differential diagnosis of GBS- AMAN should rule out:

  • infectious diseases
  • malignancy
  • disorders of the neuromuscular junction
  • spinal root inflammation due to cytomegalovirus or HIV
  • transverse myelitis
  • Lyme disease

A lumbar puncture is recommended to rule out diagnoses other than GBS- elevated protein level and normal cell counts in the CSF (termed albuminocytological dissociation) is considered a hallmark of GBS.

EMG-NCV studies also help to diagnose GBS as well as assist in identifying the subtype of the condition (AMAN, AIDP). AMAN patients tend to show decreased motor and/or sensory amplitudes , and complex neurophysiological findings with transient conduction block or slowing, which rapidly recovers during the course of the disease—a phenomenon called reversible conduction failure.[6]

The prevalence of pain can help differ between the subtypes of GBS[10] - many patients with AMAN also experience back and neck pain[11].

Prognosis[edit | edit source]

The prognosis of AMAN is worse compared to the other subtypes of GBS[12][13].

Medical Management[edit | edit source]

Medical management for AMAN combines multidisciplinary supportive medical care and immunotherapy. IVIg and plasma exchange have pleiotropic immunomodulatory effects and are considered primary treatment measures[14].

Studies have shown that patients with AMAN had better outcomes after plasma exchange than after IVIg therapy, and that plasma exchange was also the most cost-effective option[15]. Economically challenged countries have the option of small-volume plasma exchange or exchange transfusion as a low-cost therapeutic option.[15]

Physiotherapy Management[edit | edit source]

Physical therapy has shown a lot of improvement with pain management and neuromuscular efficiency. Physical therapy modalities of massage and relaxation, proprioceptive neuromuscular facilitation have shown to have positive results. [16]

Additional Details can be found on the GBS page.

References[edit | edit source]

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Lv J, Zhaori G. Collaborative studies of U.S.–China neurologists on acute motor axonal neuropathy Pediatric Investig. 2022 Mar 22;6(1):1-4.
  2. ↑ Van den Berg B, Walgaard C, Drenthen J, Fokke C, Jacobs BC, Van Doorn PA. Guillain–Barré syndrome: pathogenesis, diagnosis, treatment and prognosis. Nature Reviews Neurology. 2014 Aug;10(8):469-82.
  3. ↑ Reddy YM, Murthy JM, Osman S, et al. Guillain-Barré syndrome associated with SARS-CoV-2 vaccination: how is it different? a systematic review and individual participant data meta-analysis. Clin Exp Vaccine Res. 2023;12(2):143-155. doi:10.7774/cevr.2023.12.2.143
  4. ↑ Watrin L, Ghawché F, Larre P, Neau JP, Mathis S, Fournier E. Guillain–Barré syndrome (42 cases) occurring during a Zika virus outbreak in French Polynesia. Medicine. 2016 Apr 1;95(14):e3257.
  5. ↑ 5.0 5.1 5.2 Al-Saffar A, Al-Fatly B. Acute Motor Axonal Neuropathy in Association with Hepatitis E. Front Neurol. 2018 Feb 9;9:62. doi: 10.3389/fneur.2018.00062. PMID: 29479336; PMCID: PMC5811470.
  6. ↑ 6.0 6.1 6.2 Kuwabara S, Yuki N. Axonal Guillain-Barré syndrome: concepts and controversies. The Lancet Neurology. 2013 Dec 1;12(12):1180-8.
  7. ↑ Karbian N, Eshed-Eisenbach Y, Zeibak M, et al. Complement-membrane regulatory proteins are absent from the nodes of Ranvier in the peripheral nervous system. J Neuroinflammation. 2023;20(1):245. Published 2023 Oct 24. doi:10.1186/s12974-023-02920-9
  8. ↑ Yuki N, Hartung HP. Guillain–barré syndrome. New England Journal of Medicine. 2012 Jun 14;366(24):2294-304.
  9. ↑ Sekiguchi Y, Uncini A, Yuki N, Misawa S, Notturno F, Nasu S, Kanai K, Noto YI, Fujimaki Y, Shibuya K, Ohmori S. Antiganglioside antibodies are associated with axonal Guillain–Barré syndrome: a Japanese–Italian collaborative study. Journal of Neurology, Neurosurgery & Psychiatry. 2012 Jan 1;83(1):23-8.
  10. ↑ Ruts L, Drenthen J, Jongen JL, Hop WC, Visser GH, Jacobs BC, Van Doorn PA, Dutch GBS Study Group. Pain in Guillain-Barre syndrome: a long-term follow-up study. Neurology. 2010 Oct 19;75(16):1439-47.
  11. ↑ Latov N. Campylobacter jejuni Infection, Anti-Ganglioside Antibodies, and Neuropathy [published correction appears in Microorganisms. 2023 Mar 02;11(3):]. Microorganisms. 2022;10(11):2139. Published 2022 Oct 28. doi:10.3390/microorganisms10112139
  12. ↑ Zhang Y, Zhao Y, Wang Y. Prognostic factors of Guillain-Barré syndrome: a 111-case retrospective review. Chin Neurosurg J. 2018 Jun 18;4:14. doi: 10.1186/s41016-018-0122-y. PMID: 32922875; PMCID: PMC7398209.
  13. ↑ Seta T, Nagayama H, Katsura K, Hamamoto M, Araki T, Yokochi M, Utsumi K, Katayama Y. Factors influencing outcome in Guillain-Barré Syndrome: comparison of plasma adsorption against other treatments. Clin Neurol Neurosurg. 2005 Oct;107(6):491-6. doi: 10.1016/j.clineuro.2004.12.019. PMID: 16202823.
  14. ↑ Hughes RAC, Swan AV, van Doorn PA. Intravenous immunoglobulin for Guillain‐Barré syndrome. Cochrane Database of Systematic Reviews 2012, Issue 7. Art. No.: CD002063. DOI: 10.1002/14651858.CD002063.pub5. Accessed 09 May 2024.
  15. ↑ 15.0 15.1 Netto AB, Kulkarni GB, Taly AB, Rao GU, Periyavan S, Rao S. A comparison of immunomodulation therapies in mechanically ventilated patients with Guillain Barré syndrome. Journal of Clinical Neuroscience. 2012 Dec 1;19(12):1664-7.
  16. ↑ Shang P, Feng J, Wu W, Zhang HL. Intensive care and treatment of severe Guillain–Barré syndrome. Frontiers in Pharmacology. 2021 Apr 27;12:608130.
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