This life-threatening scenario is complicated by other medical problems such as pneumonia, severe infections, blood clots in the lungs, and bleeding in the digestive tract in 60% of those who require artificial ventilation. Autonomic dysfunction
The autonomic or involuntary nervous system, which is involved in the control of body functions such as heart rate and blood pressure, is affected in two-thirds of people with Guillain–Barré syndrome, but the impact is variable. Twenty percent may experience severe blood-pressure fluctuations and irregularities in the heart beat, sometimes to the point that the heart beat stops and requires pacemaker-based treatment. Other associated problems are abnormalities in perspiration and changes in the reactivity of the pupils. Autonomic nervous system involvement can affect even those who do not have severe muscle weakness. Causes
Infection onset
Two-thirds of people with Guillain–Barré syndrome have experienced an infection before the onset of the condition. Most commonly, these are episodes of gastroenteritis or a respiratory tract infection. In many cases, the exact nature of the infection can be confirmed. Approximately 30% of cases are provoked by Campylobacter jejuni bacteria, which cause diarrhea. A further 10% are attributable to cytomegalovirus (CMV, HHV-5). Despite this, only very few people with Campylobacter or CMV infections develop Guillain–Barré syndrome (0.25–0.65 per 1000 and 0.6–2.2 per 1000 episodes, respectively). The strain of Campylobacter involved may determine the risk of GBS; different forms of the bacteria have different lipopolysaccharides on their surface, and some may induce illness (see below) while others will not.Links between other infections and GBS are less certain.
Characteristic findings in Guillain–Barré syndrome are an elevated protein level, usually greater than 0.55 g/L, and fewer than 10 white blood cells per cubic millimeter of fluid ("albuminocytological dissociation"). This pattern distinguishes Guillain–Barré syndrome from other conditions (such as lymphoma and poliomyelitis) in which both the protein and the cell count are elevated. Elevated CSF protein levels are found in approximately 50% of patients in the first 3 days after onset of weakness, which increases to 80% after the first week.Repeating the lumbar puncture during the disease course is not recommended. The protein levels may rise after treatment has been administered. Neurophysiology
Directly assessing nerve conduction of electrical impulses can exclude other causes of acute muscle weakness, as well as distinguish the different types of Guillain–Barré syndrome. Needle electromyography (EMG) and nerve conduction studies may be performed. In the first two weeks, these investigations may not show any abnormality. Neurophysiology studies are not required for the diagnosis.Formal criteria exist for each of the main subtypes of Guillain–Barré syndrome (AIDP and AMAN/AMSAN, see below), but these may misclassify some cases (particularly where there is reversible conduction failure) and therefore changes to these criteria have been proposed. Sometimes, repeated testing may be helpful. Clinical subtypes
A number of subtypes of Guillain–Barré syndrome are recognized. Despite this, many people have overlapping symptoms that can make the classification difficult in individual cases. All types have partial forms.