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Acute Inflammatory Demyelinating Polyradiculoneuropathy

Introduction:

• Classified under the eponym Guillain-Barre syndrome (GBS)
• Other variants of GBS include Acute Motor Axonal Neuropathy (AMAN), Acute Motor and Sensory Axonal Neuropathy (ASMAN), and the Miller Fisher syndrome (MFS).
• AIDP is acute monophasic immune-mediated polyradiculoneuropathy provoked by a preceding infection

Epidemiology:

• Mean age of onset of 40 years affecting slightly more males than females of all ages, races and nationalities
• Worldwide incidence of GBS ranges from 0.6 to 4.0/100,000 people

Etiology:

• AIDP is most common form of GBS in North America, Europe and most of the developed world representing about 85% to 90% of cases
• ⅔ patients give history of antecedent respiratory tract or GI tract infection
• Campylobacter infection is most commonly observed in upto 30% cases
• Campylobacter associated GBS has worse prognosis, manifests slow recovery and with greater residual neurologic disability.
• Other precipitants include EBV, CMV, mycoplasma, pneumonia, and influenza-like illnesses
• Also has an association with HIV infection; predominantly in those who are not profoundly immunocompromised

Pathogenesis:

• Molecular Mimicry: auto-antibodies cross-react with peripheral nerve components because of sharing of cross-reactive epitopes
• Immune response can be directed towards myelin or axon of peripheral nerve
• Acute Inflammatory Demyelinating Polyradiculoneuropathy (AIDP): When directed against epitopes in myelin or schwann cell membrane; cellular + humoral immune responses are involved
• Progression of disease for about two weeks
• Nadir of disease reaches 4 weeks after initial symptoms in 90% patients
• If disease progression is more than 8 weeks, it is classified as chronic inflammatory demyelinating polyradiculoneuropathy or CIDP

Clinical Features:

• Weakness starts in the legs (90%)
• Decreased or absent reflexes in affected arms or legs (90%)
• Paresthesias accompanying weakness (>80%)
• Dysautonomia (~70%)
• Pain due to nerve root inflammation, typically in the back and extremities (two thirds of patients)
• Facial nerve Palsies (>50%)
• Oropharyngeal weakness (50%)
• Severe respiratory muscle weakness requiring ventilatory support (10%-30%)
• Oculomotor weakness (15%)
• Weakness begins in arms and facial muscles (10%)
• SIADH (5%; more in hospitalized patients)

• Unusual clinical features of GBS include: papilledema, facial myokymia, hearing loss, meningeal signs, vocal cord paralysis, and mental status changes.
• Posterior reversible encephalopathy syndrome, also called reversible posterior leukoencephalopathy syndrome has been associated with GBS in children and adults likely related to acute hypertension from dysautonomia

Electrodiagnostic findings:

Earliest findings:

As noted above, AIDP is the most common form in the United States and Europe, representing approximately 85 to 90 percent of cases. The typical clinical features are a progressive, fairly symmetric muscle weakness accompanied by absent or depressed deep tendon reflexes. (See 'Clinical features' above.)

Peripheral nerve myelin is the target of immune attack in AIDP. The immunologic basis of peripheral nerve demyelination in AIDP is discussed separately. (See "Guillain-Barré syndrome: Pathogenesis", section on 'Mechanisms'.)

Inflammatory demyelination is thought to start at the level of the nerve roots, leading to electrophysiologic conduction slowing and conduction blocks with resultant muscle weakness and back pain. Multifocal, patchy, widespread peripheral nerve demyelination follows, causing increasing paralysis. Peripheral nerve remyelination occurs relatively rapidly over several weeks to months. However, in a small percentage of patients, there is superimposed significant axonal degeneration with markedly delayed and incomplete recovery.

The earliest abnormalities seen on electrodiagnostic studies in patients with AIDP are prolonged or absent F waves and absent H reflexes, reflecting demyelination at the level of the nerve roots [20,21]. Increased distal latencies and conduction blocks with temporal dispersion of motor responses follow [22,23]. Significant slowing of nerve conduction velocities is usually not seen until the third or fourth week [23]. Sensory nerve conduction studies (NCS) reveal absent responses or slowed conduction velocities. In the first days after the onset of weakness, some patients with AIDP have a sural sparing pattern in which the sural nerve sensory response is normal, while median and ulnar nerve sensory responses are affected [21,24,25]. Sural sparing has a low to moderate sensitivity and a high specificity for AIDP compared with a diagnosis other than GBS.

Needle electromyography (EMG) of weak muscles shows reduced recruitment. Ancillary studies, such as facial NCS and blink reflexes, are occasionally helpful.

A small percentage of AIDP patients develop severe secondary axonal degeneration, and electrodiagnostic studies in these patients at three to four weeks after GBS onset show loss of motor and sensory responses on NCS with extensive denervation on needle examination.

20:34, 9 July 2019 (UTC)