Acute immune-mediated ascending demyelinating polyneuropathy; can cause respiratory failure.
Also known as: GBS, Guillain-Barré, acute inflammatory demyelinating polyneuropathy, AIDP, Miller Fisher syndrome
Overview
Acute, immune-mediated, predominantly demyelinating polyradiculoneuropathy causing rapidly progressive symmetric weakness, areflexia, and variable sensory and autonomic involvement. Most common subtype in Western countries is acute inflammatory demyelinating polyneuropathy (AIDP); axonal subtypes (AMAN, AMSAN) more common in Asia. Miller Fisher syndrome variant: ophthalmoplegia + ataxia + areflexia, associated with anti-GQ1b antibodies.
Epidemiology
Incidence ~1-2 per 100,000 per year. Affects all ages; slight male predominance. Most common cause of acute generalized weakness in developed countries.
Try two board-style Guillain-Barré Syndrome questions
Real questions from the FirstPassPA bank, with the full explanation. Pick an answer — no signup, no email.
Question 1NeurologyMedium
A 22-year-old woman develops symmetric weakness that begins in her feet and ascends over several days, 3 weeks after an episode of Campylobacter gastroenteritis. On examination she has flaccid weakness with absent deep tendon reflexes and is developing difficulty breathing. Sensation is preserved. Cerebrospinal fluid analysis shows protein 180 mg/dL with a white blood cell count of 4/mm³. Which of the following is the most likely diagnosis?
AMyasthenia gravis
BTransverse myelitis
CMultiple sclerosis
DGuillain-Barré syndrome
Reveal answer & full explanation
Correct answer: D — Guillain-Barré syndrome
AMyasthenia gravis
BTransverse myelitis
CMultiple sclerosis
DGuillain-Barré syndrome✓
Why Guillain-Barré syndrome is correct
Guillain-Barré syndrome (acute inflammatory demyelinating polyneuropathy) presents with ascending symmetric flaccid weakness and areflexia, often 1-3 weeks after Campylobacter jejuni gastroenteritis
Cerebrospinal fluid shows albuminocytologic dissociation — elevated protein (180 mg/dL) with a normal cell count (4/mm³)
Preserved sensation and early respiratory difficulty fit an evolving demyelinating polyneuropathy
Treatment is IVIG or plasmapheresis; corticosteroids are not effective
Why the others are wrong
Myasthenia gravis — causes fatigable weakness with normal reflexes and normal CSF, and is not triggered by an antecedent gastrointestinal infection (premature closure on weakness)
Transverse myelitis — produces a discrete sensory level with bowel/bladder involvement and CSF pleocytosis, none of which is present (confused-with-a-cord-syndrome)
Multiple sclerosis — a relapsing central demyelinating disease, not an acute ascending flaccid paralysis with areflexia after Campylobacter (buzzword-matching on "demyelination")
Question 2NeurologyMedium
A 58-year-old woman develops symmetric weakness that begins in her proximal legs and ascends over 10 days. On examination she has flaccid weakness, absent deep tendon reflexes, and labile blood pressure and heart rate. Cerebrospinal fluid analysis shows protein 420 mg/dL with a white blood cell count of 6/mm³. Nerve conduction studies show markedly reduced conduction velocities. Which of the following is the most important parameter to monitor?
AForced vital capacity
BSerum creatine kinase
CContinuous EEG
DSerial brain MRI
Reveal answer & full explanation
Correct answer: A — Forced vital capacity
AForced vital capacity✓
BSerum creatine kinase
CContinuous EEG
DSerial brain MRI
Why Forced vital capacity is correct
The ascending flaccid weakness, areflexia, autonomic instability, albuminocytologic dissociation, and slowed conduction velocities indicate Guillain-Barré syndrome
The major life threat is neuromuscular respiratory failure, so serial forced vital capacity (with negative inspiratory force) guides the need for intubation
A falling FVC toward roughly 20 mL/kg signals impending respiratory failure before oxygen saturation drops
IVIG or plasmapheresis is the treatment; corticosteroids are ineffective
Why the others are wrong
Serum creatine kinase — tracks muscle breakdown in myopathies and has no role in monitoring respiratory status in a neuropathy (confused-with-a-myopathy)
Continuous EEG — monitors for seizures, which are not a feature of this peripheral process (buzzword-matching on a neurologic monitor)
Serial brain MRI — Guillain-Barré syndrome is a peripheral disease, so brain imaging does not track its life-threatening complication (anchoring on central imaging)
🔒 Free preview limit reached
Keep reading — start your free trial
You've read your 2 free diagnosis previews. Create your free account to unlock the full Guillain-Barré Syndrome outline — plus all 514 diagnoses, 6,500+ board-style questions, flashcards, and an AI tutor. Your 7-day free trial includes everything, and there's no credit card required.
Antecedent infection (~2/3 of cases, 1-4 weeks before onset):
Campylobacter jejuni (most common; associated with AMAN axonal variant and anti-GM1 antibodies)
Cytomegalovirus
Epstein-Barr virus
Mycoplasma pneumoniae
Influenza
Zika virus
SARS-CoV-2 (associations reported)
Vaccinations (rare; modest signal historically with swine flu 1976; small risk with some vaccines)
Surgery, malignancy (rare)
Pathophysiology
Molecular mimicry: antibodies generated against pathogen surface antigens cross-react with epitopes on peripheral nerve myelin (gangliosides — GM1, GD1a, GQ1b). Complement activation and macrophage-mediated demyelination produce conduction block. Axonal subtypes target the nodes of Ranvier and axolemma directly. Resolves over weeks-months as nerve remyelinates.
Clinical presentation
Symptoms
Symmetric ascending weakness beginning in the legs, progressing over hours to days (peak by 2-4 weeks)
Distal paresthesias and pain (often missed by clinicians but very common — back pain especially)
Acute ascending symmetric weakness + areflexia + antecedent infection + albuminocytologic dissociation in CSF (elevated protein with normal cell count).
Acute intermittent porphyria — Abdominal pain, neuropsychiatric symptoms, dark urine, low motor function
Critical illness polyneuropathy/myopathy — Develops in ICU patients with sepsis/multiorgan failure
Heavy metal toxicity (lead, thallium, arsenic) — Subacute course, sensory >> motor, exposure history
Toxic neuropathies / drug-induced — Vincristine, isoniazid, statins; medication history
Diagnostic workup
Diagnostic criteria
Clinical: progressive symmetric weakness + areflexia, peak by 4 weeks, exclusion of alternative causes. Supportive: CSF albuminocytologic dissociation, electrodiagnostic features of demyelination.
Labs
CBC, BMP, LFTs, ESR, CRP, HIV, HBV, HCV
Antiganglioside antibodies (anti-GM1, anti-GD1a, anti-GQ1b — Miller Fisher)
Stool for Campylobacter (low yield, usually cleared by presentation)
Heavy metal screen if exposure history
Pulmonary function: bedside NIF (negative inspiratory force) and FVC every 4-8 h; intubate if FVC <20 mL/kg, NIF less negative than -30 cm H2O, or MEP <40 cm H2O ('20/30/40 rule')
Lumbar puncture: albuminocytologic dissociation (elevated protein, normal WBC <5 cells/μL) — may be normal in first week; cell count >50 suggests alternate diagnosis (HIV, sarcoid, lymphomatous infiltration)
Diagnostic algorithm
Feature
GBS
Myasthenia Gravis
Botulism
Pattern
Ascending symmetric
Fatigable, ocular/bulbar
Descending
Reflexes
Decreased/absent (early)
Normal
Decreased
Pupils
Normal (autonomic instability)
Normal
Dilated, sluggish
Antecedent
Infection 1-4 wk prior
Insidious
Canned food, honey (infants)
CSF
↑ protein, normal cells
Normal
Normal
EMG
Demyelinating, conduction block
Decremental on repetitive stim
Incremental on rapid repetitive stim
Treatment
IVIG or PLEX (not steroids)
Pyridostigmine, immunosuppression
Antitoxin, supportive
Distinguishing GBS from other acute neuromuscular weakness.
Treatment
First-line
ICU admission for any patient with autonomic instability, bulbar weakness, or rapidly progressive disease
Frequent pulmonary monitoring (FVC, NIF q4-8h); intubate at 20/30/40 thresholds — do not wait for hypoxia
IVIG 0.4 g/kg/day × 5 days (total 2 g/kg) — first-line, equivalent efficacy to PLEX, easier to administer
Plasma exchange (plasmapheresis) — 5 exchanges over 1-2 weeks; alternative first-line
Combining IVIG and PLEX provides NO additional benefit
Corticosteroids are NOT effective and may be harmful — do not use
Supportive: DVT prophylaxis, pain control (gabapentin, opioids — neuropathic pain common), bowel/bladder care, pressure ulcer prevention, PT/OT
Second-line / adjunct
Treat autonomic dysfunction: cautious BP management (avoid sudden drops), pacemaker pads available for bradyarrhythmias
Nutrition: NG/PEG if dysphagia
Psychological support (locked-in syndrome possible during peak)
Long inpatient rehab often required
Most patients improve over weeks-months; ~80% walk independently by 6 months
Loss of reflexes early is a defining feature — preserved reflexes argues against GBS.
Albuminocytologic dissociation: elevated CSF protein with normal cell count. Pleocytosis (>5-10 WBC) should make you reconsider GBS — think HIV, Lyme, sarcoid, lymphomatous meningitis.
20/30/40 rule for intubation: FVC <20 mL/kg, NIF less negative than -30, or MEP <40 cm H2O.
Steroids do NOT work in GBS — use IVIG or PLEX.
Miller Fisher variant: ophthalmoplegia + ataxia + areflexia + anti-GQ1b antibodies. Usually self-limited.
Persistent or progressive weakness >8 weeks moves the diagnosis to CIDP — which DOES respond to steroids.
References
AAN 2003 / 2012 update — Practice Parameter: Immunotherapy for Guillain-Barré Syndrome (Hughes et al., Neurology 2003; reaffirmed)
GBS Consensus — Diagnosis and Management of Guillain-Barré Syndrome — International Consensus Guideline (Leonhard et al., Nat Rev Neurol 2019)
Cochrane IVIG — Intravenous Immunoglobulin for Guillain-Barré Syndrome (Hughes et al., Cochrane Database 2014)
Brighton Criteria — Guillain-Barré Syndrome and Variants — Brighton Collaboration Case Definitions (Sejvar et al., Vaccine 2011)
Practice Neurology questions on FirstPassPA
Turn this outline into retention. 6,500+ board-style questions with an AI tutor that explains every answer — free to start, no card required.
Educational use only. This outline is a study aid for PA students and is not medical advice or a substitute for clinical judgment. FirstPassPA is an independent study tool and is not affiliated with, endorsed by, or sponsored by NCCPA or PAEA. PANCE® and PANRE® are registered trademarks of the National Commission on Certification of Physician Assistants; End of Rotation™ is a program of the Physician Assistant Education Association.