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.
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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?
ATick paralysis
BMyasthenia gravis
CFoodborne botulism
DMultiple sclerosis
EGuillain-Barré syndrome
Reveal answer & full explanation
Correct answer: E — Guillain-Barré syndrome
ATick paralysis
BMyasthenia gravis
CFoodborne botulism
DMultiple sclerosis
EGuillain-Barré syndrome✓
Why Guillain-Barré syndrome is correct
Guillain-Barré syndrome presents with ascending symmetric flaccid weakness and areflexia, often 1-3 weeks after Campylobacter jejuni gastroenteritis; AIDP is the common demyelinating form, while post-Campylobacter cases are classically the pure motor axonal variant (AMAN)
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 acute motor polyneuropathy, so serial vital capacity must be followed
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)
Tick paralysis — an attached tick's neurotoxin also produces ascending flaccid areflexic weakness with preserved sensation, but the CSF is normal rather than showing the albuminocytologic dissociation reported here, and it follows tick attachment rather than Campylobacter (confused-with-another-ascending-paralysis)
Multiple sclerosis — a relapsing central demyelinating disease, not an acute ascending flaccid paralysis with areflexia after Campylobacter (buzzword-matching on "demyelination")
Foodborne botulism — a recent gastrointestinal illness, flaccid weakness with preserved sensation, and respiratory compromise can point to an ingested toxin, but botulinum toxin causes a descending paralysis that begins with cranial nerve signs such as ptosis, diplopia, and dysphagia, often with poorly reactive pupils, and the CSF is normal rather than showing the albuminocytologic dissociation reported here (confused-with-a-descending-paralysis)
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?
AContinuous pulse oximetry
BSerial serum sodium
CForced vital capacity
DSerial nerve conduction studies
ESerum creatine kinase
Reveal answer & full explanation
Correct answer: C — Forced vital capacity
AContinuous pulse oximetry
BSerial serum sodium
CForced vital capacity✓
DSerial nerve conduction studies
ESerum creatine kinase
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)
Serial serum sodium — hyponatremia from SIADH is a real complication of Guillain-Barré syndrome and is worth following, but it is not the parameter that determines the need for intubation, so it is not the most important one here (real-but-lower-priority)
Serial nerve conduction studies — repeating a study already performed tracks the demyelinating lesion rather than ventilatory reserve, and the electrophysiologic changes lag the clinical course, so they cannot time airway protection (confused-with-tracking-the-lesion)
Continuous pulse oximetry — it watches the respiratory system, which is why it tempts, but in neuromuscular respiratory failure oxygen saturation is preserved until late, especially on supplemental oxygen, because hypoventilation and fatigue come first; a normal saturation gives false reassurance and cannot time intubation the way a falling FVC does (confused-with-hypoxemic-failure)
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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 in Ten Steps (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)
EAN/PNS 2023 — European Academy of Neurology/Peripheral Nerve Society Guideline on Diagnosis and Treatment of Guillain-Barré Syndrome (van Doorn et al., Eur J Neurol 2023;30:3646-3674)
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