GBS is a syndrome; i.e., a collection of symptoms and signs that have different causes and different pathologies. The common factors linking the different forms of GBS are that is is an autoimmune disease that affects the peripheral nervous system (the nerves in the head, body and limbs but outside the brain and spinal cord) and that it evolves rapidly, over a few weeks. The commonest form of GBS is also known as acute inflammatory demyelinating polyneuropathy (AIDP) because the immune attack damages the myelin sheath that insulates the nerve fibres (axons). “Polyneuropathy” just means many nerves and essentially is synonymous with the more commonly used “neuropathy”. Another common form of GBS is acute motor axonal neuropathy (AMAN) that looks identical at the bedside but the immune attack is directed against the axons. Some forms of GBS are restricted in their distribution, affecting only a few nerves. The best known of these is called the Miller Fisher syndrome (MFS) in which the immune attack primarily affects the nerves controlling the eye muscles.
GBS is a treatable disease and the outcome is usually good even for those with severe weakness. About 70% of patients recover full strength while some are left with variable degrees of weakness, mainly in the form of foot drop and hand weakness. 50%-80% will have residual fatigue or poor stamina which can last for years, even though their muscle strength returns to normal, and others will have residual pain. Patients rarely die of GBS and those that do are nearly always older (over 75) or have other medical problems. The most important treatment is general medical support to prevent complications. Specific treatment of GBS speeds recovery, however it does not impact on the final degree of recovery.
GBS is an autoimmune disease. Our immune system normally protects us against disease by killing harmful invading pathogens, but with GBS, this normally protective response is hijacked and instead attacks our own nerves. What causes this to happen is not precisely known but about 70% of cases follow an identifiable event, usually an infection. In NZ, the commonest identified infection is caused by an organism called Campylobacter jejuni, a common cause of food poisoning. NZ has one of the highest rates of C. jejuni infection in the world and due to this GBS incidence is almost double that of other western countries.