Guillain-Barré syndrome (GBS) represents a spectrum of rare acute immune-related polyneuropathies with varying features and presentations. It is divided into 2 main subtypes: demyelinating and axonal. Demyelinating forms include acute inflammatory demyelinating polyneuropathy (AIDP) and clinical variant Miller Fisher syndrome (MFS). Axonal forms include acute motor axonal neuropathy (AMAN) and acute motor-sensory axonal neuropathy (AMSAN).

AMAN is characterized by symmetric limb weakness, facial and oropharyngeal muscle weakness, areflexia, and respiratory insufficiency. A variant is AMSAN, which involves damage to axons of sensory neurons in addition to those of motor neurons and is characterized by acute onset of quadriparesis, distal sensory loss, areflexia, and respiratory insufficiency. There can also be autonomic dysfunction in both diseases. AMAN typically progresses to nadir more rapidly than AIDP.

The exact etiology is unclear, but GBS typically presents days to weeks after an infection, most commonly Campylobacter jejuni. Other reported triggers include cytomegalovirus, influenza, Epstein-Barr virus, HIV, and Japanese encephalitis. GBS has also been reported in patients with probable Zika virus infection in South America, French Polynesia, Latin America, and the Caribbean and in patients with Oropouche virus infection in Cuba. Rarely, GBS has been associated with surgery or immunization. There have been rare reports of GBS occurring about 2 weeks after having the Johnson & Johnson (Janssen) COVID-19 vaccine.

AMAN occurs more frequently in China and Japan. It often progresses more rapidly than AIDP. Recovery is unpredictable; some patients recover completely in days, while others have slow and incomplete recovery.