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  • Updated 04.16.2018
  • Released 11.27.2003
  • Expires For CME 04.16.2021

Acute motor axonal neuropathy

Introduction

This article includes discussion of acute motor axonal neuropathy, Chinese paralytic syndrome, axonal GBS, acute motor-sensory axonal neuropathy (AMSN), acute inflammatory demyelinating polyradiculoneuropathy (AIDP), and Miller Fisher syndrome (MFS). The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.

Overview

Acute motor axonal neuropathy is the most frequent axonal variant of Guillain-Barré syndrome (GBS) and is often used synonymously with the term axonal GBS. This review describes clinical and electrodiagnostic features of acute motor axonal neuropathy and compares it with the acute inflammatory demyelinating polyradiucloneuropathy variant of Guillain-Barré syndrome. Pathology and pathogenesis of this disorder are discussed to highlight the theme of molecular mimicry.

Key points

• Acute motor axonal neuropathy is a variant of Guillain-Barré syndrome with predominant motor axon dysfunction or injury, and it is strongly associated with antecedent Campylobacter jejuni infection and the presence of anti-ganglioside antibodies.

• In North America and Europe, acute motor axonal neuropathy is much less frequent than acute inflammatory demyelinating polyradiucloneuropathy.

• Electrodiagnostic studies (at times serial exams) are required to distinguish axonal variants, including acute motor axonal neuropathy, from demyelinating forms of Guillain-Barré syndrome.

• Acute motor axonal neuropathy does not necessarily signify a poor prognosis as patients with nodal or motor nerve terminal dysfunction or injury without significant axon degeneration can recover quickly.

• Treatment should include intravenous immunoglobulins or plasmapheresis as well as supportive therapy.

Historical note and terminology

Guillain-Barré syndrome is a pathophysiologically heterogeneous peripheral nerve disorder of autoimmune origin. There are several variants of this condition, and a classification of this syndrome is included in Table 1. Acute motor axonal neuropathy variant of Guillain-Barré syndrome is a paralytic condition presenting with an acute, ascending, and flaccid paralysis. This is distinguished from acute inflammatory demyelinating polyneuropathy primarily by electrophysiological studies. In 1986, Feasby and colleagues reported 5 cases of Guillain-Barré syndrome with electrically inexcitable motor nerves. Autopsy on 1 patient showed significant and marked axonal degeneration in the ventral roots and peroneal nerves without demyelination. Feasby and colleagues were the first to suggest a possible variant of Guillain-Barré syndrome characterized by acute axonal neuropathy (34).

In 1981, Baoxun and colleagues reported 156 patients admitted to a hospital in Beijing, China for Guillain-Barré syndrome, of which 68.6% had onset between July and October. In addition, 75.6% were less than 30 years of age, with a majority coming from rural areas (15). These observations suggested seasonal propensity for children to develop Guillain-Barré syndrome in China. McKhann and colleagues used the terminology “Chinese paralytic syndrome” to refer to children and young adults from predominantly rural areas presenting with acute flaccid paralysis in seeming epidemics during summer and fall months. Electrodiagnostic studies in 22 of 37 patients showed reduction in compound muscle action potential amplitudes, suggesting axonal abnormalities. There was little to no prolongation of distal motor latencies or slowing of motor nerve conduction velocities suggesting demyelination, except in 1 patient who also had abnormal sensory studies; these finding suggest this patient had acute inflammatory demyelinating polyneuropathy (87).

McKhann and colleagues later coined the phrase “acute motor axonal neuropathy” instead of Chinese paralytic syndrome (86).

Acute motor-sensory axonal neuropathy was later used by Griffin and colleagues to differentiate cases of Guillain-Barré syndrome with electrodiagnostic features of axonal damage involving both motor and sensory fibers, such as Feasby and colleagues reported in 1986 (41). Although Griffin and colleagues suggest patients with acute motor-sensory axonal neuropathy may have a more severe disease than acute motor axonal neuropathy, they also recognize similar pathological characteristics of the motor and sensory fibers. They suggest the disorders may be within the spectrum of the same disease.

Table 1. Classification of Guillain-Barré syndrome

Paralytic forms

Demyelinating electrophysiology

Acute inflammatory demyelinating polyradiculoneuropathy (AIDP)

Axonal electrophysiology

Acute motor axonal neuropathy (AMAN)
Acute motor-sensory axonal neuropathy (AMSAN)
AIDP with secondary axonal degeneration

Regional or focal paralytic forms

Fisher syndrome
Oropharyngeal
Acute ophthalmoplegia

Non-paralytic forms

Sensory ataxic variant
Acute pandysautonomia

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