Guillain-Barré syndrome other diagnostic studies


 * Associate Editors-In-Chief: Priyamvada Singh, MBBS [mailto:psingh@perfuse.org]

Overview
Guillain-Barré syndrome (GBS) is an acute, autoimmune, polyradiculoneuropathy affecting the peripheral nervous system, usually triggered by an acute infectious process. Nerve conduction study may show prolonged distal latencies, conduction slowing, conduction block, and temporal dispersion of compound action potential in demyelinating cases. Forced vital capacities also help in taking decisions regarding ventilators.

Electrodiagnostic tests
ECD is used almost every time to verify symptoms, but because of the acute nature of the disease, they may not become abnormal until after the first week of onset of signs and symptoms. The following tests may be ordered:
 * Electrodiagnostics -
 * Electromyography (EMG)-EMG tests the electrical activity in muscles. It may show that nerves do not react properly to stimulation.
 * Nerve conduction study
 * (NCS) may show prolonged distal latencies, conduction slowing, conduction block, and temporal dispersion of compound action potential in demyelinating cases.
 * In primary axonal damage, the findings include reduced amplitude of the action potentials without conduction slowing.
 * Nerve motor action potentials may be decreased. Compound muscle action potential (CMAP) amplitude may be decreased.
 * The extent of decreased action potentials correlates with prognosis. Prolonged distal latencies may be present. Abnormal H-reflex may be noted.
 * Needle examination shows profuse and early denervation potentials also support the conclusion that there has been axonal injury

Pulmonary function test

 * Pulmonary function test (Maximal inspiratory pressures, maximal expiratory pressures and forced vital capacities) should be done regularly to monitor patients' respiratory performances and any need for ventilator.
 * Forced vital capacities also help in taking decisions regarding ventilators.

Muscle biopsy

 * It is not commonly done but may be used as an adjunct to rule out myopathies (in cases of diagnostic dilemmas)