Guillian Barre Syndrome

Question 1

What is the pathophysiology behind GBS?

Answer 1

• Aka acute inflammatory demyelinating polyneuropathy (AIDP), the commonest type of GBS.
Pathophysiology
  
  • Patchy demyelination of nerve roots though autoimmune T cell destruction.
  • Due to molecular mimicry post infection.

Question 2

What causes GBS?

Answer 2

• URTI (1 in 2): CMV, EBV, Mycoplasma.
  
  • Gastroenteritis: Campylobacter jejuni.
  • Idiopathic (1 in 3).
  • Rare causes: HIV seroconversion, possibly flu vaccine (but if so, extremely rare and benefits of vaccine far outweigh the risk).

Question 3

What is the time course of GBS?

Answer 3

• 2-4 week progressive phase, then recovery.
  
  • Chronic inflammatory demyelinating polyneuropathy (CIDP) is its chronic counterpart, and the label applied when GBS symptoms fail to plateau and begin improvement within 8 weeks.

Question 4

What are the signs and symptoms of GBS?

Answer 4

• Typically presents around 2-4 weeks post infection.
Ascending motor and sensory symptoms:
  
  • Starts with distal paraesthesia and proximal weakness.
  • Limbs are first affected. Usually starts with legs, but can be arms too.
  • Proceeds to affect trunk, respiratory muscles, and cranial nerves (especially CN7).
  • Usually symmetrical.
• Other features:
  
  • ↓Reflexes (95%).
  • Pain: back, limb.
  • Autonomic symptoms: ↓sweating, arrhythmias especially ↑HR, ↑BP or ↓BP, ileus.
  • 15% have a descending pattern e.g. cranial nerves affected first.
• AIDP is the commonest type. Other variants are:
  
  • Miller Fischer syndrome: descending paralysis. Triad of ophthalmoplegia, ataxia (limb/gait), and areflexia. Anti-GQ1b Ab +ve.
  • Acute motor sensory axonal neuropathy: acute quadriparesis, areflexia, distal sensory loss, and respiratory insufficiency. Poor recovery.
  • Acute motor axonal neuropathy: symmetrical limb weakness, areflexia, and face weakness. Commoner in China.
• DDx: Acute neurogenic ventilatory failure
  
  • Guillain-Barré syndrome.
  • Myasthenia gravis.
  • Polymyositis
  • MND
  • Botulism
  • Polio

Question 5

Which investigations should be done in suspected GBS?

Answer 5

• Bloods:
  
  • U+E: SIADH may occur in up to 50%, likely due to dysautonomia.
  • LFT: occasionally ↑ALT and ↑AST (mechanism unclear).
  • Peripheral and central nervous system Ab screen.
• Consider stool culture to check for recent C. jejuni infection.
Special tests:
  
  • Nerve conduction studies are the key diagnostic test, showing slowed conduction. 95% sensitive.
  • LP: ↑protein. Often normal in first week, so its use early on is mainly to exclude other diagnoses.
  • Spirometry: carry out regularly to look for signs of respiratory compromise (↓FVC).
• Imaging:
  
  • MRI to rule out other causes e.g. disc problem.
  • ECG: may show arrhythmias, heart block.

Question 6

How is GBS managed?

Answer 6

• Supportive treatment, including HR and BP control. In some cases this is sufficient.
  
  • IVIg or plasma exchange, especially if severe (e.g. non-ambulatory).
  • ITU transfer if ↓FVC.
  • DVT prophylaxis.
  • There is little evidence for steroids.
• Intravenous immunoglobulin (IVIg)
Pooled IgG of >1000 donors.
Mechanism
Unclear, but may include:
  
  • Neutralises cytokines.
  • Modulates Fc receptor-mediated phagocytosis.
  • Stimulates complement removal of all Ab including host auto-Ab.

Question 7

What are the side-effects of intravenous immunoglobulin?

Answer 7

• Infection from donors.

* Anaphylaxis if IgA deficient. Plasma exchange is an alternative for these patients.

Question 8

What is the prognosis for GBS?

Answer 8

• 80% recover, including those who become fully paralysed.
  
  • 10% can’t walk at 1 year.
  • 10% mortality.