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  • Updated 12.07.2023
  • Released 11.27.2003
  • Expires For CME 12.07.2026

Acute motor axonal neuropathy



Acute motor axonal neuropathy is the most frequent axonal variant of Guillain-Barré syndrome and is often used synonymously with the term “axonal Guillain-Barré syndrome.” This review describes clinical and electrodiagnostic features of acute motor axonal neuropathy and compares it with the acute inflammatory demyelinating polyradiculoneuropathy variant of Guillain-Barré syndrome. The 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 (GBS) 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 polyradiculoneuropathy.

• Electrodiagnostic studies (preferably serial) 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.

• Novel therapeutic approaches under current investigation include inhibition of complement activation and the modulation of neonatal Fc receptors (FcRn) to alleviate neuroinflammation in acute motor axonal neuropathy and other Guillain-Barré syndrome subtypes.

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 five cases of Guillain-Barré syndrome with electrically inexcitable motor nerves. Autopsy on one 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 (42).

In 1981, Baoxun and colleagues reported on 156 patients admitted to a hospital in Beijing, China, for Guillain-Barré syndrome; 68.6% of the patients had onset between July and October (18). In addition, 75.6% were less than 30 years of age, with the majority from rural areas. These observations suggest a 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 one patient who also had abnormal sensory studies. These findings indicate that this patient had acute inflammatory demyelinating polyneuropathy (109). McKhann and colleagues later coined the phrase “acute motor axonal neuropathy” instead of Chinese paralytic syndrome (108).

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 (51). 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. The disorders may be within the same disease spectrum.

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
Acute ophthalmoplegia

Non-paralytic forms

Sensory ataxic variant
Acute pandysautonomia

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