Guillain-Barré Syndrome - Autoimmune Processes

GUILLAIN-BARRÉ SYNDROME

Guillain-Barré syndrome is an autoimmune attack of the periph-eral nerve myelin. The result is acute, rapid segmental demyeli-nation of peripheral nerves and some cranial nerves, producing ascending weakness with dyskinesia (inability to execute volun-tary movements), hyporeflexia, and paresthesias (numbness). In 66% of cases, there is a predisposing event, most often a respira-tory or gastrointestinal infection, although vaccination, pregnancy, and surgery have also been identified as antecedent events (Bella Chad, 1998). Infection with Campylobacter jejuni (a relatively common gastrointestinal bacterial pathogen) precedes Guillain-Barreé syndrome in a few cases (Ho & Griffin, 1999; Lindenbaum, Kissel & Mendel, 2001).

The antecedent event usually occurs 2 weeks before symptoms begin. Weakness usually begins in the legs and progresses upward for about 1 month. Maximum weakness varies but usually in-cludes neuromuscular respiratory failure and bulbar weakness. The duration of the symptoms is variable: complete functional recovery may take up to 2 years (Hickey, 2003). Any residual symptoms are permanent and reflect axonal damage from de-myelination.

The annual incidence of Guillain-Barré is 0.6 to 1.9 cases per 100,000. Eighty-five percent of patients recover with minimal residual symptoms. Severe residual deficits occur in up to 10% of patients. Residual deficits are most likely in patients with rapid disease progression, those who require mechanical ventilation, or those 60 years of age or older. Death occurs in 3% to 8% of cases, resulting from respiratory failure, autonomic dysfunction, sepsis, or pulmonary emboli (Bella & Chad, 1998).

Pathophysiology

Myelin is a complex substance that covers nerves, providing in-sulation and speeding the conduction of impulses from the cell body to the dendrites. The cell that produces myelin in the pe-ripheral nervous system is the Schwann cell. In Guillain-Barré the Schwann cell is spared, allowing for remyelination in the recovery phase of the disease.

Guillain-Barré is the result of a cell-mediated immune attack on peripheral nerve myelin proteins (Ho & Griffin, 1999). The best-accepted theory is that an infectious organism contains an amino acid that mimics the peripheral nerve myelin protein. The immune system cannot distinguish between the two proteins and attacks and destroys peripheral nerve myelin. Studies indicate that an exact location within the peripheral nervous system, the ganglioside GM1b, is the most likely target of the immune attack (Yuki, Ang, Koga et al., 2000). With the autoimmune attack there is an influx of macrophages and other immune-mediated agents that attack myelin, cause inflammation and destruction, and leave the axon unable to support nerve conduction.

Clinical Manifestations

Classic Guillain-Barré begins with muscle weakness and dimin-ished reflexes of the lower extremities. Hyporeflexia and weakness progress and may result in quadriplegia. Demyelination of the nerves that innervate the diaphragm and intercostal muscles re-sults in neuromuscular respiratory failure. Twenty-five percent of patients will require mechanical ventilation within 18 days of symptom onset (Bella & Chad, 1998). Sensory symptoms include paresthesias of the hands and feet and pain related to the de-myelination of sensory fibers.

Cranial nerve demyelination can result in a variety of clinical manifestations. Optic nerve demyelination may result in blind-ness. Bulbar muscle weakness related to demyelination of the glossopharyngeal and vagus nerves results in an inability to swallow or clear secretions. Vagus nerve demyelination results in autonomic dysfunction, manifested by instability of the cardio-vascular system. The presentation is variable and may include tachycardia, bradycardia, hypertension, or orthostatic hypoten-sion. The symptoms of autonomic dysfunction occur and resolve rapidly. Guillain-Barré does not affect cognitive function or level of consciousness.

While the classic clinical features include areflexia and as-cending weakness, variation in presentation occurs. There may be a sensory presentation, with progressive sensory symptoms, an atypical axonal destruction, and the Miller-Fisher variant, which includes paralysis of the ocular muscles, ataxia, and areflexia (Ho & Griffin, 1999).

Assessment and Diagnostic Findings

The patient presents with symmetric weakness, diminished re-flexes, and upward progression of motor weakness. A history of a viral illness in the previous few weeks suggests the diagnosis. Changes in vital capacity and negative inspiratory force are as-sessed to identify impending neuromuscular respiratory failure. Serum laboratory tests are not useful in the diagnosis. However, elevated protein levels are detected in CSF evaluation, without an increase in other cells. Evoked potential studies demonstrate a progressive loss of nerve conduction velocity (Bella & Chad, 1999).

Medical Management

Because of the possibility of rapid progression and neuromuscular respiratory failure, Guillain-Barré is a medical emergency, re-quiring intensive care unit management. Careful assessment of changes in motor weakness and respiratory function alert the clinician to the physical and respiratory needs of the patient. Respiratory therapy or mechanical ventilation may be necessary to support pulmonary function and adequate oxygenation. Mechanical ventilation may be required for an extended period. The patient is weaned from mechanical ventilation when the res-piratory muscles can again support spontaneous respiration and maintain adequate tissue oxygenation.

Other interventions are aimed at preventing the complications of immobility. These may include the use of anticoagulant agents and thigh-high elastic compression stockings or sequential com-pression boots to prevent thrombosis and pulmonary emboli.

Plasmapheresis and IVIG are used to directly affect the pe-ripheral nerve myelin antibody level. Both therapies decrease cir-culating antibody levels and reduce the amount of time the patient is immobilized and dependent on mechanical ventilation. Studies indicate that IVIG and plasmapheresis are equally effective in treating Guillain-Barré (Bella & Chad, 1999; Winer, 2002).

The cardiovascular risks posed by autonomic dysfunction re-quire continuous ECG monitoring. Tachycardia and hypertension are treated with short-acting medications such as alpha-adrenergic blocking agents. Hypotension is managed by increasing the amount of IV fluid administered. The use of short-acting agents is important because autonomic dysfunction is very labile.