Guillain-Barré Syndrome (GBS), is an acquired immune-mediated inflammatory disorder of the peripheral nervous system (e.g. not the brain and spinal cord). It is also called acute inflammatory demyelinating polyneuropathy, acute idiopathic polyradiculoneuritis, acute idiopathic polyneuritis and Landry's ascending paralysis.

The pathologic hallmark of the disease is myelin loss of peripheral nerves due to an acute and progressive inflammation of unknown cause. It is suggested that it is an autoimmune disease, in which the sufferer's immune system is triggered into damaging the nerve covering. There is some support for this in that half of all cases occur soon after a microbial infection or respiratory or gastrointestinal viral infection. Many cases developed in people who received the 1976 swine flu vaccine.

Peripheral nerves originate in the spinal cord and proceed to their target tissues (mainly muscle, skin and all internal organs). Their most proximal parts emerging from the spinal cord are called nerve roots and the inflammation in most (but not all) typical Guillain-Barré syndrome cases starts in these roots. Therefore, this condition is also referred to as acute polyradiculoneuritis.

GBS is a rare - affecting about 1 to 2 people in every 100,000 per year. It does not discriminate with regard to the age or sex of sufferers.

About one half of patients have a history of preceding viral infection. Guillain-Barré syndrome may also be associated with immunizations, recent surgery or trauma, pregnancy, Hodgkin's disease and connective tissue diseases. The most frequently associated viral agents are cytomegalovirus (CMV), HIV, measles and herpes simplex virus. A bacteria called Campylobacter jejuni has recently been shown to be closely related with certain subtypes of the disease.

Extensive damage of myelin causes disturbances in peripheral nerve functions, which can be classified as motor (affecting the muscle), sensory (affecting the skin) or autonomic (affecting the internal organs). Therefore, patients usually show two or more of the following symptoms: weakness (often symmetrical, in ascending fashion, leading to respiratory failure in 1/3 of cases), decreased sensation (numbness, loss of position sense), severe fluctuations in blood pressure, irregularities of heart rate, constipation and incontinence. Additional symptoms may be blurred vision, difficulty moving facial muscles, difficulty swallowing, and drooling.

The diagnosis is established by electromyography examination, nerve conduction studies (NCS), and cerebrospinal fluid (CSF) examination. Electromyography and NCS show slowing of conduction velocities, indicating myelin loss; CSF examination reveals high protein content with usually normal or slightly elevated cell count, indicating severe nerve damage. These findings are usually prominent after the first week of the disease, so the clinical symptoms and findings are more valuable in the early stages.

Recent studies on the disease have demonstrated that approximately 80% of the patients have myelin loss, whereas, in the remaining 20%, the pathologic hallmark of the disease is indeed axon loss. The cases indicating the demyelinating form (AIDP) are called "acute motor and sensory axonal neuropathy" (AMSAN); the cases showing only motor symptoms (diffuse weakness) are called "acute motor axonal neuropathy" (AMAN). In a different and infrequent variant called Miller Fisher syndrome, patients develop ataxia, loss of tendon reflexes, and difficulty moving eye muscles but not weakness or sensory loss. All variants of Guillain-Barré syndrome are now supposed to be an autoimmune disease caused by antibodies against a variety of gangliosides found in abundant amounts in the peripheral nerve tissue.

The symptoms are ascending weakness with abnormal sensations and then paralysis of the legs, arms, face and possibly breathing muscles. It is rarely fatal but there is no direct cure and recovery may need care in a intensive care unit and can take years (although people can recover in a few weeks as as well).

Supportive care with monitoring of all vital functions is the cornerstone of successful management. Because the immune mechanisms play a role in pathogenesis, plasma exchange or intravenous immunoglobulins may improve the outcome. Although the corticosteroids may be used in treatment, they are not usually considered the drug of first choice because they may occasionally worsen the symptoms.

Approximately 80% of patients have a complete recovery and about 5-10% recover with severe disability. However this is a grave disease and despite all improvements in treatment and supportive care, the death rate among patients with this disease is still about 2-3% even in the best intensive care units.

The disease was first described by the French physician Jean Landry in 1859. In 1916, Georges Guillain, Jean Alexandre Barré and Andre Strohl discovered the key diagnostic abnormality of increased spinal fluid protein production, but normal cell count.