Guillain-Barré Syndrome (GBS) — Examination Question Bank

Pathogenesis, Microbiology & Diagnostic Classification

Question	Answer
1. Detail the molecular mimicry pathogenesis of Guillain-Barré Syndrome.	GBS is an acute, post-infectious, immune-mediated polyradiculoneuropathy driven by molecular mimicry between infectious microbial surface antigens and peripheral nerve gangliosides. - The most classical antecedent organism is Campylobacter jejuni (enteritis), followed by CMV, EBV, Mycoplasma pneumoniae, and Zika virus. - The lipo-oligosaccharide (LOS) outer envelope of C. jejuni shares identical molecular carbohydrate epitopes with human peripheral nerve gangliosides (GM1, GD1a, GQ1b, GD1b). - The immune system generates anti-LOS antibodies that cross-react with gangliosides on the axolemma (nodes of Ranvier) or Schwann cell myelin sheath. - Antibody binding activates the classical complement cascade, depositing membrane attack complexes (C5b-9), leading to macrophage recruitment, myelin breakdown (AIDP), or direct nodal axonal transection (AMAN/AMSAN).
2. Classify the clinical and electrophysiological subtypes of GBS.
3. What are the Brighton Diagnostic Criteria for GBS?	Evaluates the certainty of diagnosis from Level 1 (highest) to Level 4: - Clinical Features: Bilateral and flaccid weakness of limbs; decreased or absent deep tendon reflexes in weak limbs; monophasic illness course with nadir reached between 12 hours and 28 days. - Laboratory & Electrophysiology: - CSF: Albuminocytological Dissociation (CSF total protein elevated above laboratory normal; CSF cell count $<50 ext{ cells/mm}^3$, typically $<5-10$). - Nerve Conduction Studies: Electrophysiological findings consistent with AIDP or AMAN/AMSAN. - Level 1 (Definite): All clinical features + CSF albuminocytological dissociation + NCS confirmation. - Level 2: Clinical features + CSF dissociation OR NCS findings. - Level 3: Clinical features alone. - Level 4: Unclassified / Other disorders ruled out.

Bedside Monitoring, Respiratory Failure & CSF Dynamics

Question	Answer
4. How do you assess Impending Respiratory Failure at the bedside in a child with GBS?	Bedside clinical and physiological indicators of diaphragmatic and intercostal paralysis: 1) Single-Breath Count: Ask the child to take a maximal inspiration and count aloud at a steady pace of 2 numbers per second during expiration. Normal $>20-25$. A count $<15$ indicates compromised vital capacity ($<50\%$ normal); $<10$ indicates critical respiratory fatigue. 2) Paradoxical Abdominal Breathing: Inward motion of the anterior abdominal wall during inspiration (confirms diaphragmatic paralysis; accessory neck muscles pull chest up while flaccid diaphragm is sucked cephalad). 3) Weak Ineffective Cough & Swallowing Incompetence: Inability to clear saliva or airway secretions. 4) The "Rule of 20 / 30 / 40": - Forced Vital Capacity (FVC) $<20 ext{ mL/kg}$ (normal $>60 ext{ mL/kg}$). - Maximal Inspiratory Pressure (MIP) $<-30 ext{ cmH2O}$ (normal $<-70 ext{ cmH2O}$). - Maximal Expiratory Pressure (MEP) $<40 ext{ cmH2O}$ (normal $>100 ext{ cmH2O}$). - Action: If any of these thresholds are breached, electively transfer to PICU for planned endotracheal intubation before emergency asphyxial arrest occurs!
5. Explain "Albuminocytological Dissociation" in CSF: Timing and Significance.	- Hallmark CSF finding: Markedly elevated protein concentration with a normal white blood cell count ($<5-10 ext{ mononuclear cells/mm}^3$). - Caused by massive protein leakage from inflamed, demyelinated spinal nerve roots into the subarachnoid space without concomitant intrathecal cellular pleocytosis. - VIVA TRAP on Timing: In the first 48 to 72 hours of weakness, CSF protein is completely NORMAL in up to $50\%$ of children! CSF protein begins to rise toward the end of the first week and peaks during weeks 2 to 4. - Clinical Pearl: A normal lumbar puncture on Day 2 of illness NEVER excludes GBS! Do not delay immunotherapy while waiting for CSF protein to rise!
6. What is Dysautonomia in GBS and how is it managed?	Dysautonomia occurs in up to $60\%$ of severe GBS cases due to demyelination of sympathetic and parasympathetic autonomic fibers: - Manifestations: Persistent sinus tachycardia, abrupt severe sinus bradycardia / asystole, paroxysmal hypertension, severe orthostatic hypotension, anhidrosis or profuse diaphoresis, paralytic ileus, and urinary retention. - Management: - Continuous cardiac rhythm and intra-arterial BP monitoring in PICU. - Bradycardia / Asystole: Atropine at bedside; temporary transvenous pacing for severe refractory blocks. - Labile Hypertension: Use short-acting, titratable IV agents (Labetalol, Esmolol, or Nicardipine). Avoid long-acting vasodilators that trigger profound rebound hypotension! - Hypotension: Judicious fluid boluses; low-dose vasopressors (phenylephrine/norepinephrine).

Immunotherapy, Controversies & Viva Traps

Question	Answer
7. Compare Intravenous Immunoglobulin (IVIG) vs Plasma Exchange (PE) in GBS.	- Both IVIG and Plasma Exchange are equally effective in accelerating motor recovery, reducing duration of mechanical ventilation, and improving functional outcomes. - IVIG Protocol: $2 ext{ g/kg}$ total dose, administered either as $1 ext{ g/kg/day}$ for 2 consecutive days (preferred in pediatrics) or $0.4 ext{ g/kg/day}$ for 5 days. - Advantages: Easily administered through peripheral veins, widely available, does not require central venous access, hemodynamically better tolerated in unstable children. - Plasma Exchange (PE) Protocol: 4 to 5 exchanges ($50 ext{ mL/kg}$ per session) over 7 to 14 days with albumin replacement. - Requires large-bore dual-lumen central venous catheter; risk of line sepsis, hypocalcemia, and hemodynamic instability in autonomic dysfunction. - VIVA TRAP: Combining IVIG followed immediately by PE (or vice versa) provides NO additive benefit and is NOT recommended! Choose ONE modality based on availability and venous access.
8. VIVA TRAP: What is the role of Corticosteroids in Guillain-Barré Syndrome?	VIVA TRAP: Corticosteroids (oral or intravenous) have NO therapeutic role in GBS and are strictly CONTRAINDICATED as monotherapy! - Multiple large multicenter randomized controlled trials (Cochrane Reviews) demonstrated that oral or IV corticosteroids do not accelerate recovery, do not improve long-term disability, and oral steroids may actually delay motor recovery and increase adverse effects. - Why? Steroids suppress macrophage clearance of degraded myelin debris and inhibit Schwann cell remyelination!
9. Counter-Question Chain: "How do you clinically differentiate GBS from Acute Transverse Myelitis (ATM) at bedside?"