Guillain-Barré syndrome (GBS) is one of those “don’t-miss” neuro emergencies on USMLE: a rapidly progressive, ascending weakness that can silently become a respiratory failure case if you don’t recognize it early. The good news: the testable patterns are consistent, and once you know the core variants, questions feel like free points.
The 10-second one-liner (memorize this)
GBS = immune-mediated demyelinating (or axonal) polyradiculoneuropathy → ascending weakness + areflexia after an infection, with albuminocytologic dissociation in CSF.
Visual / mnemonic device (quick-hit)
“G-B-S”
- G = Going up (ascending weakness)
- B = Back pain + autonomic Blood pressure swings (dysautonomia)
- S = Spinal fluid: high protein, normal cells (albuminocytologic dissociation)
Bonus hook: Think “Boots → Belt → Breath”
Weakness climbs from legs (boots) → hips/torso (belt) → diaphragm (breath).
Core diagnosis pattern (USMLE-style)
Typical clinical picture
- Symmetric ascending weakness over days to weeks
- Areflexia/hyporeflexia is high-yield (LMN pattern)
- Often follows:
- Campylobacter jejuni (classic)
- Viral illness (e.g., CMV, EBV, influenza)
- Less commonly post-vaccination (boards may mention temporal association)
Key complications you must anticipate
- Respiratory failure (watch the diaphragm!)
- Autonomic instability: arrhythmias, labile BP, urinary retention/ileus
Comparison table: GBS and its major variants
| Feature | AIDP (Classic GBS) | Miller Fisher syndrome | AMAN | AMSAN |
|---|---|---|---|---|
| Full name | Acute inflammatory demyelinating polyradiculoneuropathy | Variant of GBS | Acute motor axonal neuropathy | Acute motor-sensory axonal neuropathy |
| Primary pathology | Demyelination of peripheral nerves/roots | Often demyelinating; distinct antibody association | Axonal (motor) | Axonal (motor + sensory) |
| Classic triad / hallmark | Ascending weakness + areflexia | Ophthalmoplegia + ataxia + areflexia | Pure motor weakness | Motor weakness + prominent sensory involvement |
| Sensory symptoms | Mild/variable (paresthesias common) | Usually minimal | Minimal | Prominent |
| Common trigger association | Post-infectious; C. jejuni common | Often post-infectious | C. jejuni strongly associated | Often post-infectious |
| Antibodies (high-yield) | No single classic antibody | Anti-GQ1b | Anti-GM1 (classically tested, esp with C. jejuni) | Can be ganglioside Abs |
| NCS/EMG pattern | Slowed conduction, prolonged distal latencies, conduction block | Similar demyelinating features | Low CMAP amplitude, relatively preserved conduction velocity | Low CMAP + sensory involvement (SNAP changes) |
| Prognosis | Often good recovery with treatment | Often good | Variable; can be severe | Often more severe, slower recovery |
Exam tip: If the stem screams ophthalmoplegia + ataxia + areflexia, don’t overthink—go Miller Fisher (anti-GQ1b).
Diagnostic workup (what the test wants)
CSF (lumbar puncture)
- Albuminocytologic dissociation:
- ↑ protein with normal WBC count
- Timing nuance: CSF protein may be normal early (first week) → rises later
NCS/EMG
- Helps distinguish:
- Demyelinating (AIDP) vs axonal variants (AMAN/AMSAN)
Bedside respiratory monitoring (high yield “next step”)
- Forced vital capacity (FVC) and negative inspiratory force to assess impending respiratory failure
- Don’t wait for O₂ sat to drop—hypercapnia/ventilatory failure can happen before desaturation.
Treatment: what actually changes outcomes
First-line disease-modifying therapy
- IVIG or plasmapheresis (similar efficacy)
- Best when started early in significant weakness or rapid progression
What NOT to do
- Steroids do NOT help in classic GBS (common trick)
Supportive care (frequent test points)
- Respiratory support if needed (intubate early if declining FVC)
- DVT prophylaxis (immobility risk)
- Manage autonomic dysfunction (telemetry, treat arrhythmias, cautious BP management)
High-yield differentiators (GBS vs common look-alikes)
| Condition | Key clue | Reflexes | Sensory level? | Localization |
|---|---|---|---|---|
| GBS | Ascending weakness after infection; autonomic symptoms | ↓/absent | No | Peripheral nerves/roots |
| Myasthenia gravis | Fluctuating fatigable weakness; ocular/bulbar | Normal | No | NMJ |
| Botulism | Descending paralysis, pupillary involvement, autonomic sx | Variable | No | Presynaptic NMJ |
| Transverse myelitis / cord compression | Back pain + sensory level + bowel/bladder | Often ↑ below lesion (UMN signs) | Yes | Spinal cord |
| Tick paralysis | Rapid ascending weakness; exposure history | ↓ | No | Neurotoxin effect |
Quick checkpoint:
- Areflexia + ascending weakness = GBS
- Sensory level + UMN signs = spinal cord problem, not GBS.
Rapid-fire USMLE facts (flashcard style)
- Most common cause of acute flaccid paralysis in the US = GBS
- Most common trigger tested = Campylobacter jejuni
- CSF: ↑ protein, normal WBC (albuminocytologic dissociation)
- Treatment: IVIG or plasmapheresis (not steroids)
- Most dangerous complication: respiratory failure + arrhythmias
- Miller Fisher: ophthalmoplegia + ataxia + areflexia, anti-GQ1b