Acute inflammatory demyelinating polyneuropathy (AIDP) is an autoimmune process that is characterized by progressive areflexic weakness and mild sensory changes. Sensory symptoms often precede motor weakness. About 20% of patients end up with respiratory failure. Many variants exist. In the West, the most common presentation is a subacute ascending paralysis. This is associated with distal paresthesias and loss of deep tendon reflexes. Progression is often maximal by the end of 4 weeks, then the condition usually plateaus before slowly improving. In 1859, Landry described 10 cases characterized by ascending paralysis and sensory changes.
During World War I, Guillain, Barré, and Strohl described a series of patients with a similar presentation and decreased or absent deep tendon reflexes. They also described albuminocytologic dissociation in the cerebrospinal fluid (CSF), ie, increased CSF protein in the absence of increased WBCs. This allowed them to differentiate AIDP from poliomyelitis, the most common acute paralytic syndrome of that era. (AIDP often is referred to as Guillain-Barré syndrome [GBS]).
Myelin breakdown and axonal degeneration were observed in nerve biopsies from patients with AIDP by Haymaker and Kernohan in 1949.  An allergic etiology was suggested by Krucke in 1955 after he observed lymphocytic infiltrates within biopsy specimens.  An autoimmune process was supported by Waksman and Adams when they created the experimental allergic neuritis model by injecting peripheral nerve tissue into rodents. 
Acute inflammatory neuropathies encompass groups of heterogeneous disorders characterized by pathogenic immune-mediated hematogenous leukocyte infiltration of peripheral nerves, nerve roots or both, with resultant demyelination or axonal degeneration or both, and the pathogenesis of these disorders remains elusive.
The recent isolation and characterization of human endoneurial endothelial cells that form the blood-nerve barrier provides an opportunity to elucidate leukocyte-endothelial cell interactions critical to the pathogenesis of inflammatory neuropathies at the interface between the systemic circulation and peripheral nerve endoneurium.
Acute inflammatory demyelinating polyneuropathy is believed to be caused by an immunologic attack that is directed against myelin components. This results in a demyelinating polyneuropathy. Both cellular and humoral immune mechanisms appear to play a role. Early inflammatory lesions consist of a lymphocytic infiltrate that is adjacent to segmental demyelination. Macrophages are more prominent several days later.
The peripheral nerve changes consist of varying degrees of perivascular edema, accumulations of mononuclear cells, and paranodal and less commonly, segmental demyelination. They are often multifocal with some predilection for the nerve roots, sites of entrapment, and distal ends. In the axonal variant of Guillain-Barré syndrome, axonal degeneration often predominates. Severe Guillain-Barré syndrome is often associated with axonal degeneration as well, which results in wallerian degeneration. Axonal degeneration occurs either as a primarily axonal process or as a bystander-type axonal degeneration, associated with demyelination. Rarely, the pathologic process extends into the central nervous system.
As the regeneration occurs, nerve sprouting and increased scarring often results.
With electron microscopy, macrophages are observed stripping off the myelin sheath. Humoral molecules such as antimyelin antibodies and complement likely contribute to the process by directing macrophages to Schwann cells by opsonization. Indeed, complement and antibodies have been found to coat the myelin sheath. The changes are observed in nerve roots, peripheral nerves, and cranial nerves. In acute motor axonal neuropathy (AMAN, an AIDP variant), deposited complement is found at the nodes of Ranvier, while myelin often is left undamaged.
Damage to the myelin sheath leads to segmental demyelination. This results in decreased nerve conduction velocity and, at times, conduction block. In this current review, AIDP refers to the more common demyelinating form unless otherwise specified.
Acute inflammatory demyelinating polyneuropathy is the most common acquired demyelinating polyneuropathy. The incidence is 0.6-1.7 cases per 100,000 per year. No significant seasonal variation has been noted.
Frequency is not well documented. Of 2 predominant Guillain-Barré syndrome subtypes, a demyelinating subtype (AIDP) predominates in the United States and Europe, and axonal subtype (AMAN) is the predominant form in China. Previous clinical studies suggested that AMAN also occurs in Mexican children.  Similar outbreaks have been reported in Mexico, Spain, and Jordan.
In 3 large studies, mortality rate ranged from 2-6%.
In general, death is due to complications of ventilation. Causes include cardiac arrest, pulmonary embolus, sepsis, bronchospasm, pneumothorax, adult respiratory distress syndrome (ARDS), and dysautonomia.
More than 75% of patients have complete or near-complete recovery with no deficit or only mild residual fatigue and distal weakness.
Other patients, almost all of whom required ventilation, report severe dysesthesias or moderately severe distal weakness as residual symptoms. About 15% of patients end up with significant neurological residuals.
Acute inflammatory demyelinating polyneuropathy occurs in all races and in all regions of the world.
The male-to-female ratio is 1.1-1.7:1.
Patients have ranged in age from 2 months to 95 years.
In the United States, age distribution is apparently bimodal, with most patients presenting from 15-35 years or 50-75 years.
In China (and other countries), frequent outbreaks in children aged 2-12 years have been reported.
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