9.3 Guillain-Barré Syndrome & Autoimmune Neurologic Conditions

Guillain-Barré Syndrome and Myasthenia Gravis

Autoimmune neurological conditions involve the body's immune system erroneously attacking components of the nervous system. Guillain-Barré Syndrome (GBS) represents an acute inflammatory demyelinating polyneuropathy affecting the peripheral nervous system, while Myasthenia Gravis (MG) is a chronic disorder targeting the neuromuscular junction. Both conditions share a significant risk of respiratory failure, necessitating intense clinical vigilance.

Guillain-Barré Syndrome (GBS)

GBS is an acute, rapidly progressive, and potentially fatal form of polyneuritis. It is characterized by segmental demyelination of the peripheral nerves and cranial nerves. The demyelination prevents the normal transmission of electrical impulses along the sensorimotor nerve roots.

Etiology and Pathophysiology

GBS is widely considered a post-infectious, immune-mediated disease. Most patients report a viral respiratory or gastrointestinal infection 1 to 3 weeks prior to the onset of neurological symptoms. Campylobacter jejuni is the most frequently identified infectious trigger. The immune response, initially mounted against the invading pathogen, exhibits molecular mimicry and cross-reacts with the gangliosides present on the myelin sheaths of peripheral nerves, leading to macrophage-mediated demyelination.

Clinical Presentation

The hallmark of classic GBS (Acute Inflammatory Demyelinating Polyradiculoneuropathy - AIDP) is symmetrical, ascending, flaccid paralysis.

• Weakness typically begins in the lower extremities and progresses upward to the trunk, upper extremities, and cranial nerves.
• Deep tendon reflexes are diminished or absent (areflexia).
• Sensory symptoms, such as paresthesias and pain (often severe, aching pain in the back and legs), are common but less prominent than motor weakness.
• Autonomic dysfunction is a frequent and dangerous complication, manifesting as cardiac dysrhythmias, orthostatic hypotension, labile blood pressure, and bowel/bladder dysfunction.

Cranial nerve involvement, particularly CN VII (facial nerve), occurs in many patients, leading to bilateral facial weakness. Involvement of the lower cranial nerves (IX, X, XII) leads to dysphagia and an inability to manage secretions.

Diagnostics

Diagnosis is based on the clinical presentation and confirmed by two key studies:

1. Lumbar Puncture: CSF analysis reveals a classic finding known as albuminocytologic dissociation—a markedly elevated CSF protein level without a corresponding elevation in the white blood cell count (pleocytosis).
2. Electromyography (EMG) and Nerve Conduction Studies (NCS): Demonstrate marked slowing of nerve conduction velocity, indicative of demyelination.

Medical and Nursing Management

GBS is a medical emergency primarily due to the risk of respiratory failure as the ascending paralysis reaches the intercostal muscles and the diaphragm.

Respiratory Monitoring: The nurse must perform rigorous respiratory assessments, measuring Negative Inspiratory Force (NIF) and Forced Vital Capacity (FVC) frequently (e.g., every 2-4 hours). A NIF of less than -20 cm H2O or an FVC falling below 15-20 mL/kg strongly indicates impending respiratory failure, necessitating elective intubation and mechanical ventilation before a crisis occurs.

Immunomodulatory Therapy: Treatment aims to halt the autoimmune destruction. Two primary therapies are equally effective:

1. Intravenous Immunoglobulin (IVIG): Typically administered at a dose of 0.4 g/kg/day for 5 days. It provides donor antibodies that neutralize the pathogenic autoantibodies.
2. Plasmapheresis (Plasma Exchange): Involves removing the patient's plasma and replacing it, effectively filtering out the circulating autoantibodies.

Note: Corticosteroids have not been shown to be effective in GBS and are not recommended.

Nursing care also focuses on preventing complications of immobility (DVT prophylaxis, pressure injury prevention), managing severe neuropathic pain (often with gabapentin or tricyclic antidepressants), and providing intensive psychological support due to the terrifying nature of acute paralysis in an awake, alert patient.

Myasthenia Gravis (MG)

Myasthenia Gravis is a chronic autoimmune disorder affecting the neuromuscular junction. It is characterized by fluctuating weakness and rapid fatigability of voluntary skeletal muscles.

Pathophysiology

In MG, the immune system produces antibodies against the acetylcholine receptors (AChR) located on the postsynaptic membrane of the neuromuscular junction. These antibodies destroy the receptors, block acetylcholine from binding, and facilitate receptor endocytosis. Consequently, fewer receptors are available for acetylcholine, resulting in impaired muscle contraction. The thymus gland is frequently abnormal in MG patients (thymoma or thymic hyperplasia) and is believed to be the source of autoantibody production.

Clinical Presentation

The defining feature of MG is muscle weakness that worsens with exertion and improves with rest.

• Initial symptoms often involve the ocular muscles, leading to ptosis (drooping eyelids) and diplopia (double vision).
• Bulbar involvement affects the muscles of the face, chewing, swallowing, and speech, presenting as a mask-like facial expression, dysphagia, and dysarthria.
• Generalized weakness affects the proximal muscles of the limbs and neck.

Diagnostics

• Serology: Detection of anti-AChR antibodies is highly specific.
• Tensilon (Edrophonium) Test: Intravenous injection of a short-acting acetylcholinesterase inhibitor. In MG, this transiently prevents the breakdown of acetylcholine, resulting in a dramatic, short-lived improvement in muscle strength.
• EMG: Shows a decremental response to repetitive nerve stimulation.

Management and Crises

Medical management relies on acetylcholinesterase inhibitors, primarily pyridostigmine (Mestinon), which prolongs the action of acetylcholine at the synapse. Immunosuppressants (corticosteroids, azathioprine) and thymectomy are utilized for long-term disease modification.

The most critical nursing consideration in MG is the differentiation and management of two life-threatening crises, both presenting with severe respiratory muscle weakness:

1. Myasthenic Crisis:

• Cause: An exacerbation of the disease process or inadequate medication (under-dosing of pyridostigmine).
• Symptoms: Severe muscle weakness, respiratory distress, dysphagia, absent cough reflex.
• Tensilon Test Result: Administration of edrophonium results in improvement of muscle strength.
• Treatment: Respiratory support (intubation/ventilation), increase acetylcholinesterase inhibitors, IVIG or plasmapheresis.

2. Cholinergic Crisis:

• Cause: Over-medication with acetylcholinesterase inhibitors, leading to an excess of acetylcholine at the neuromuscular junction, causing continuous depolarization and subsequent muscle block.
• Symptoms: Severe muscle weakness, respiratory distress, plus symptoms of parasympathetic overstimulation: salivation, lacrimation, urination, defecation, GI cramping, emesis (SLUDGE syndrome), miosis (constricted pupils), and bradycardia.
• Tensilon Test Result: Administration of edrophonium results in worsening of weakness or no improvement.
• Treatment: Respiratory support, immediately discontinue all acetylcholinesterase inhibitors, administer atropine (to reverse muscarinic overstimulation).