Guillain-Barre Syndrome

Molecular mechanisms

• Molecular mimicry: Infection-induced antibodies cross-react with gangliosides on peripheral nerve myelin (particularly GM1, GD1a, GQ1b epitopes in Campylobacter jejuni infection)
• Antibody-mediated demyelination via complement activation (C1q, C3b, MAC deposition at nodes of Ranvier)
• Direct axonal injury in acute inflammatory demyelinating polyradiculoneuropathy (AIDP) and axonal variants (AMAN, AMSAN)

Cellular mechanisms

• T-cell infiltration of nerve roots and peripheral nerves (CD8+ T lymphocytes predominate)
• Macrophage-mediated myelin stripping and paranodal disruption
• Breakdown of blood-nerve barrier with increased vascular permeability

Pathophysiologic consequences

• Conduction block at demyelinated segments causing weakness (AIDP phenotype—most common, ~90%)
• Axonal degeneration with wallerian degeneration and prolonged recovery (AMAN/AMSAN phenotypes—more common in Asian populations)
• Proximal nerve root involvement causing ascending paralysis pattern (distinguishes from most neuropathies)
• Autonomic dysregulation from involvement of parasympathetic and sympathetic fibers, resulting in cardiac arrhythmias, blood pressure lability, and sphincter dysfunction

Infectious triggers (60-70% of cases)

• ***Campylobacter jejuni* infection** (most common preceding infection; associated with axonal variants and worse prognosis)
• Cytomegalovirus (CMV), particularly in immunocompromised patients
• Epstein-Barr virus (EBV)
• Influenza A and other respiratory viruses
• Zika virus (emerging association with severe GBS)
• Mycoplasma pneumoniae
• Haemophilus influenzae
• Hepatitis A and E
• HIV (acute seroconversion illness)

Non-infectious triggers

• Vaccinations (historically influenza vaccine; swine flu pandemic vaccine association debated)
• Surgery or trauma (2-3 weeks prior)
• Malignancy (especially lymphoma, Hodgkin disease)
• Systemic lupus erythematosus and other autoimmune diseases
• Medications (rare: rarely implicated)

Risk factors for severe disease

• Advanced age (>60 years)
• Rapid disease progression (<7 days to nadir)
• High disability at nadir
• Ventilator requirement
• C. jejuni seropositivity
• Axonal electrophysiologic pattern

Cardinal symptoms

• Ascending paralysis beginning distally in lower extremities and progressing proximally over days to weeks
• Symmetric weakness (distinguishing feature from most neuropathies)
• Paresthesias and dysesthesias often preceding weakness by hours to days (painful burning sensations common)
• Weakness reaching nadir within 2 weeks in 90% of cases
• Bilateral facial weakness (50% of cases; may be first sign)
• Bulbar symptoms: dysarthria, dysphagia (25-35%)
• Respiratory weakness from diaphragmatic paralysis or intercostal muscle involvement (30%)

Physical examination findings

• Areflexia or hyporeflexia (hallmark finding; nearly universal, even with preserved strength early)
• Flaccid weakness with preserved sensation (sensory examination typically normal or shows mild impairment)
• Cranial nerve involvement: CN VII (facial nerve) most common; CN IX, X, XI also affected
• Normal cognition and consciousness (distinguishes from encephalitis)
• Autonomic signs: tachycardia, hypertension or hypotension, facial flushing, diaphoresis, urinary retention
• Pain in back, shoulders, and limbs (often severe, requiring analgesia)
• Ataxia (if predominantly sensory involvement)
• Ophthalmoplegia (Miller Fisher variant)

Clinical diagnostic criteria (Brighton Collaboration)

• Required: Progressive weakness of ≥2 limbs AND areflexia/hyporeflexia
• Supportive: Ascending progression, symptoms beginning in lower extremities, relative symmetry, mild sensory signs, cranial nerve involvement, autonomic dysfunction, recovery pattern

Cerebrospinal fluid (CSF) analysis (lumbar puncture)

• Albuminocytologic dissociation: elevated protein (>45 mg/dL) with normal white cell count (<50 cells/μL), the classic CSF finding
• Protein typically 50-500 mg/dL (may be normal in first week, then rises)
• Lymphocytic predominance (up to 10-15 cells/μL); neutrophils early
• Normal glucose (CSF-to-serum ratio ~0.5-1.0)
• Caveat: Early GBS (<1 week) may have normal CSF; repeat LP after 1 week if clinical suspicion high

Electrodiagnostic testing (EMG/NCS) - essential for confirmation

• AIDP phenotype (demyelinating, 85-90%):
• Segmental demyelination with conduction blocks
• Prolonged distal latencies
• Slowed conduction velocities (<70% lower limit normal)
• Prolonged/absent F waves
• Preserved amplitudes (until late)

• AMAN phenotype (motor axonal, 5-10%):
• Reduced compound muscle action potential (CMAP) amplitudes
• Normal or near-normal conduction velocities
• Preserved sensory nerve action potentials (SNAPs)—critical distinguishing feature

• AMSAN phenotype (motor and sensory axonal):
• Reduced CMAPs AND SNAPs
• Denervation (fibrillations) on needle EMG in acute phase

Serologic testing

• Anti-ganglioside antibodies (GM1, GD1a, GQ1b): positive in 50-60% of cases; not required for diagnosis but support it
• **Anti-*C. jejuni* antibodies**: epidemiologically useful but not diagnostic

Imaging

• Spinal MRI: enhancement of cauda equina/nerve roots (gadolinium, T1-weighted); not specific but supportive
• Chest X-ray: assess for aspiration risk, baseline respiratory assessment
• Brain MRI: only if clinical confusion suggests alternative diagnosis (MS, encephalitis)

Differential diagnosis considerations (imaging/testing to exclude)

• CNS demyelination (MS): MRI brain/spinal cord with lesion burden, CSF oligoclonal bands
• Myelitis/myelopathy: spinal cord signal change on MRI
• Spinal cord compression: MRI spinal cord compression sign
• Botulism: preserved pupil reactivity, normal EMG pattern
• Tick paralysis: careful skin examination, normal CSF/EMG

Immunotherapy (cornerstone of management)

• Intravenous immunoglobulin (IVIG) - First-line:
• Dose: 2 g/kg body weight divided over 3-5 days (standard: 0.4 g/kg/day × 5 days)
• Mechanism: Fc-receptor saturation, reduced complement activation, immune modulation
• Efficacy: Shortens time to recovery and reduces ventilator dependence by ~50%
• Initiate within 2 weeks of symptom onset (most effective within first 7 days)
• Monitor: Renal function (risk of acute kidney injury, especially in diabetes), volume status, aseptic meningitis (rare)

• Plasma exchange - Equivalent first-line alternative:
• 1.5 plasma volumes exchanged, 5 sessions over 7-10 days
• Mechanism: Removes circulating antibodies and immune complexes
• Comparable efficacy to IVIG; preferred if IVIG unavailable or contraindicated
• Complications: Thrombosis, infection, hemodynamic instability; requires central venous access
• Relative contraindication: Severe cardiovascular disease, sepsis

• Combination therapy: IVIG + plasma exchange—marginal benefit over monotherapy; reserved for fulminant presentations

Adjunctive treatment

• Corticosteroids: High-dose methylprednisolone (1 g IV daily × 3-5 days) remains controversial; meta-analyses show no benefit over IVIG alone; NOT recommended as monotherapy
• Pain management: Aggressive analgesia with opioids (neuropathic pain often severe and disabling); gabapentin or pregabalin for neuropathic pain
• Supportive care (critical):
• Mechanical ventilation for respiratory weakness (FVC <15 mL/kg or accessory muscle use)
• Deep vein thrombosis prophylaxis: sequential compression devices, pharmacologic thromboprophylaxis (LMWH)
• Stress ulcer prophylaxis (H2 blocker or PPI)
• Passive range-of-motion exercises, early mobilization
• Nutritional support (enteral feeding if dysphagia)
• Catheterization and monitoring for urinary retention
• Cardiovascular monitoring: continuous telemetry in ICU, frequent vital sign checks (autonomic instability)

Monitoring parameters

• Vital capacity (FVC) or negative inspiratory force (NIF): trends guide ventilatory support
• Electrolytes, renal function, liver function (IVIG/plasma exchange baseline and during therapy)
• Serum osmolality if SIADH suspected (rare)
• Cardiac rhythm (autonomic dysfunction may cause arrhythmias)

Respiratory compromise

• Acute respiratory failure requiring mechanical ventilation (30% of hospitalized patients)
• Mechanism: Diaphragmatic paralysis, intercostal muscle weakness, bulbar dysfunction with aspiration
• Management: Early anticipatory intubation (do not wait for severe hypoxemia); aggressive airway protection
• Prolonged mechanical ventilation in 10-15% of cases

Autonomic dysfunction

• Cardiac arrhythmias: tachycardia, bradycardia, atrial fibrillation, asystole (especially during suctioning or manipulation)
• Hypertensive or hypotensive episodes (fluctuating blood pressure)
• Syndrome of inappropriate antidiuretic hormone (SIADH): hyponatremia, concentrated urine
• Management: Continuous cardiac monitoring in ICU, avoid triggers (suctioning, manipulation), cautious fluid management

Infections

• Hospital-acquired pneumonia (aspiration, ventilator-associated pneumonia): leading infectious complication
• Urinary tract infection from prolonged catheterization
• Sepsis as secondary complication

Pain syndromes

• Severe neuropathic pain in 50% of patients; can be disabling and prolonged
• Back and shoulder pain (mechanical from immobility + neuropathic)
• Chronic pain in 10-15% at 1 year

Other complications

• Recurrent GBS (3-5% relapse); can occur years after initial illness
• Contractures and joint immobility from prolonged paralysis
• Hypokalemia (shift into cells), hyperkalemia (rhabdomyolysis if severe)
• Rhabdomyolysis and acute kidney injury (rare)
• Pulmonary embolism (immobility)
• Delirium (ICU psychosis)

Miller Fisher variant-specific

• Ophthalmoplegia may progress to respiratory failure (similar prognosis to classic GBS)

Natural history

• Progression phase: Median 10-14 days to nadir (range 1-27 days); 90% reach nadir within 2 weeks
• Plateau phase: Days to weeks of stable weakness
• Recovery phase: Begins weeks to months after nadir; average duration 6-12 months
• Most patients achieve functional recovery; 60-70% walk independently within 6 months

Prognostic factors for worse outcomes

• Severe disease at nadir (NIHSS score, disability grade ≥4)
• Rapid progression to severe weakness (<7 days)
• Ventilator requirement (indicates worst prognosis)
• Age >60 years
• Preceding C. jejuni infection (axonal pattern)
• Axonal electrophysiologic pattern (AMAN/AMSAN)
• Delayed immunotherapy initiation
• Diarrhea as preceding illness (marker of C. jejuni)

Favorable prognostic factors

• Mild disease at nadir
• Young age
• Demyelinating pattern (AIDP)
• Rapid response to immunotherapy

Disability at 1 year

• 20-30% have persistent disability (difficulty walking, weakness)
• 5-10% have severe disability
• 3-7% mortality (even with treatment); primarily from respiratory failure, autonomic complications, or nosocomial infection
• Mortality higher in elderly and with axonal variants

Post-GBS syndrome

• Fatigue, weakness, pain persist in 10-15% at 5 years despite clinical recovery
• Psychological sequelae (depression, PTSD) common

• Most important fact: Ascending paralysis + areflexia + elevated CSF protein with normal cells = GBS until proven otherwise; clinical recognition is paramount as early immunotherapy improves outcomes

• Classic board presentation: "Young patient with recent Campylobacter gastroenteritis now with progressive leg weakness, hyporeflexia, and albuminocytologic dissociation on LP—give IVIG"

• Red flag finding: Preserved sensation despite motor weakness distinguishes GBS from myelopathy or spinal cord compression (which also present with weakness + areflexia)

• EMG phenotype mnemonic—"AIDP vs AMAN":
• AIDP: Demyelination (slowed velocities, conduction blocks, prolonged latencies)—85% in developed countries
• AMAN: Axonal—reduced CMAP but preserved SNAPs (key differentiator)—more common post-*C. jejuni* in developing countries

• Common exam trap: Early GBS may have normal CSF in first week; clinical judgment required—do not delay treatment pending repeat LP

• Ventilator decision: Intubate early and prophylactically when vital capacity <15 mL/kg or negative inspiratory force more negative than -30 cm H₂O; do NOT wait for respiratory failure

• Autonomic pitfall: Suctioning/routine care can precipitate life-threatening arrhythmias or profound hypotension; anticipate and manage aggressively with cardiac monitoring

• Treatment pearl: IVIG vs. plasma exchange equivalence—choose IVIG if renal disease, cardiac disease, or no central access available; both reduce time to recovery by ~50%

• No role for: Corticosteroids alone (no benefit); antibiotics (infection trigger, not treatment); anticoagulation as primary therapy

• Miller Fisher variant red flag: Ophthalmoplegia + ataxia + areflexia; anti-GQ1b antibodies positive in 90%; same recovery pattern as GBS but starts in brainstem

• Recurrence awareness: 3-5% of patients develop recurrent GBS years later; always consider in returning patients with acute ascending paralysis