Pathophysiology: The pathophysiology of GBS is complex. GBS is considered to be an autoimmune disease triggered by a preceding bacterial or viral infection. Campylobacter jejuni, cytomegalovirus, Epstein-Barr virus and Mycoplasma pneumoniae are commonly identified antecedent pathogens.
In the acute motor axonal neuropathy (AMAN) form of GBS, the infecting organisms probably share homologous epitopes to a component of the peripheral nerves (molecular mimicry) and, therefore, the immune responses cross-react with the nerves causing axonal degeneration; the target molecules in AMAN are likely to be gangliosides GM1, GM1b, GD1a and GalNAc-GD1a expressed on the motor axolemma. In the acute inflammatory demyelinating polyneuropathy (AIDP) form, immune system reactions against target epitopes in Schwann cells or myelin result in demyelination; however, the exact target molecules in the case of AIDP have not yet been identified.
The body's immune system begins to attack the body itself, The immune responses causes a cross-reaction with the neural tissue. When myelin is destroyed, destruction is accompanied by inflammation. These acute inflammatory lesions are present within several days of the onset of symptoms. Nerve conduction is slowed and may be blocked completely. Even though the Schwann cells that produce myelin in the peripheral nervous system are destroyed, the axons are left intact in all but the most severe cases. After 2-3 weeks of demyelination, the Schwann cells begin to proliferate, inflammation subsides, and re-myelination begins.
While GBS is the most common cause of acute paralysis, the exact pathogenesis is still unclear. The progression of demyelination appears different in AMAN type of GBS versus AIDP type. Nadir is the point of greatest severity and patients with AMAN type reach it earlier.
Epidemiology:Incidence: The annual incidence of GBS in the USA is 1.2-3 per 100,000 inhabitants; GBS has been reported throughout the world. Most studies show annual incidence figures similar to those in the United States.
•Age: The annual mean rate of hospitalizations in the United States related to GBS increases with age, being 1.5 cases per 100,000 population in children under 15 years of age, and peaking at 8.6 cases per 100,000 population in 70-79 year olds