Neurology · Topic 18 of 22
Guillain-Barré Syndrome
Neurology · neuromuscular emergency
Guillain-Barré Syndrome
Ascending flaccid weakness with lost reflexes: trend vital capacity, watch for autonomic storms, and give IVIG or plasma exchange — never steroids.
Key numbers
Check FVC every 6–8 hoursintubate VC < 15 mL/kg
IVIG 0.4 g/kg daily for 5 days0.4 g/kg/day × 5 d
20/30/40 rule flags respiratory failureVC < 20 mL/kg
01 · Look forAscending flaccid weakness with absent reflexes
GBS is an acute inflammatory polyneuropathy: relatively symmetric flaccid weakness, usually starting in the legs and ascending, with lost deep tendon reflexes, mild distal paresthesias and spared sphincters.
02 · WatchCheck FVC every 6–8 hours
Admit and measure forced vital capacity every 6–8 hours; intubate when vital capacity falls below 15 mL/kg. About 20% of patients need mechanical ventilation.
03 · GiveIVIG 0.4 g/kg daily for 5 days
Treat with IVIG 0.4 g/kg daily for 5 days or plasma exchange (200–250 mL/kg over 5 sessions) — equally effective; IVIG is usually chosen because it is easier to give.
01
What it is
Core ideaMiller Fisher: ophthalmoplegia, ataxia, areflexiaThe Miller Fisher variant presents with ophthalmoplegia, ataxia and areflexia rather than limb weakness.
02
Causes & risk factors
Why it happensFollows infection by 5 days–3 weeksAbout two-thirds of cases start 5 days to 3 weeks after an infection (Campylobacter jejuni, CMV, EBV, Mycoplasma, Zika, COVID-19), surgery or vaccination; immune checkpoint inhibitors can cause a similar syndrome.
03
Diagnosis & monitoring
Work-up20/30/40 rule flags respiratory failureRespiratory failure is likely when vital capacity is < 20 mL/kg, maximal inspiratory pressure < 30 cmH₂O or maximal expiratory pressure < 40 cmH₂O; plan elective intubation before crisis.
Admit to ICU for bulbar or respiratory weaknessAdmit to the ICU for evolving respiratory distress, severe autonomic dysfunction, severe swallowing difficulty or weak cough, or rapidly progressive weakness; inability to lift the head off the pillow parallels diaphragm weakness.
CSF: high protein, normal cell countCSF shows albuminocytologic dissociation — raised protein with a normal cell count — but protein is normal in 30–50% in the first week; more than 50 cells/µL suggests another diagnosis.
04
Do right now
In this orderFirst moves
1
→Check FVC every 6–8 hoursintubate VC < 15 mL/kg
2
→Telemetry for autonomic instability
3
→IVIG 0.4 g/kg daily for 5 days0.4 g/kg/day × 5 d
4
LMWH prophylaxis, pain control, early PT
Why each step
Check FVC every 6–8 hoursAdmit and measure forced vital capacity every 6–8 hours; intubate when vital capacity falls below 15 mL/kg. About 20% of patients need mechanical ventilation.
Telemetry for autonomic instabilityDysautonomia causes blood pressure swings, arrhythmias, SIADH, ileus and urinary retention; monitor ECG, heart rate and blood pressure — most GBS deaths are cardiovascular or respiratory, often in the recovery phase.
IVIG 0.4 g/kg daily for 5 daysTreat with IVIG 0.4 g/kg daily for 5 days or plasma exchange (200–250 mL/kg over 5 sessions) — equally effective; IVIG is usually chosen because it is easier to give.
LMWH prophylaxis, pain control, early PTSupportive care: LMWH for DVT prophylaxis, treatment of frequent neuropathic or radicular pain, swallow screening, passive range of motion and early physical therapy to prevent contractures.
05
Management
OrdersNerve conduction studies; early normal doesn't excludeOrder nerve conduction studies and EMG to support the diagnosis (slowed conduction, demyelination), but normal results in the first week must not delay treatment.
06
Red flags & don'ts
Avoid harmDo not give corticosteroids in GBS avoidGlucocorticoids do not help GBS — eight randomized trials showed no benefit and oral steroids worsened outcome — so they are not given.
07
The rules
Know theseStart IVIG within 2 weeks, PLEX within 4Start IVIG or plasma exchange when the patient cannot walk 10 m unaided, and consider it for rapid progression, bulbar, autonomic or respiratory weakness; trials show benefit within 2 weeks (IVIG) or 4 weeks (PLEX).
No PLEX after IVIG; no second IVIGDo not follow IVIG with plasma exchange (it removes the IVIG) and do not routinely give a second IVIG course — neither improves outcome.
08
Guillain-Barré or myasthenia gravis?
Commonly confused| Pattern | Ascending, relatively symmetric flaccid weakness |
|---|---|
| Reflexes | Lost |
| Sensation | Mild distal paresthesias |
| Eyes | Ophthalmoparesis only in the Miller Fisher variant |
09
Commonly confused
Tell apartProgression beyond 8 weeks suggests CIDPWeakness usually peaks within 2 weeks and almost always by 4 weeks; reaching nadir within 24 hours or after 4 weeks suggests another diagnosis, and deterioration beyond 8 weeks suggests acute-onset CIDP.
10
More detail
ReferenceShow 6 reference facts
Mimics: botulism (fixed dilated pupils, normal sensation), tick paralysis (ascending, sensation spared), West Nile (fever, asymmetric paralysis), transverse myelitis or cord compression (sensory level, early bladder dysfunction).
Up to 22% need ventilation in the first week; the Erasmus GBS Respiratory Insufficiency Score (EGRIS) estimates that risk from onset-to-admission time, facial or bulbar weakness and MRC sum score.
Features that cast doubt on GBS: marked persistent asymmetry, bladder or bowel dysfunction at onset, fever at onset, severe respiratory failure with little limb weakness, or a sensory level.
Mortality is about 3–10% in the ten-steps guideline (under 4% in Merck's cited cohort); 60–80% walk independently at 6 months, and 6–10% deteriorate again after initial treatment (treatment-related fluctuation).
Send HIV, hepatitis serology and serum protein electrophoresis; use spine MRI in atypical cases to exclude cord compression and look for nerve root enhancement.
Myasthenia gravis differs from GBS: weakness fluctuates and worsens with exertion, ptosis and diplopia are common, and reflexes and sensation stay normal.
Trend the vital capacity every 6–8 hours and intubate before it falls below 15 mL/kg.
Sources · Merck Manual Professional — Guillain-Barré Syndrome (GBS) · Leonhard SE et al. Diagnosis and management of Guillain–Barré syndrome in ten steps. Nat Rev Neurol 2019;15:671–683 · Merck Manual Professional — Myasthenia Gravis · Starter sheet built from the verified AGACNP fact map (facts reviewed 2026-10-15).