Guillain-Barré Syndrome

• Molecular mimicry and epitope spreading: Preceding infections (particularly Campylobacter jejuni, which occurs in ~30% of GBS cases) express lipopolysaccharides structurally similar to gangliosides present on peripheral nerve myelin and axons. Antibodies generated against pathogenic epitopes cross-react with these neural antigens. In classic demyelinating GBS (AIDP, 70-80% of cases in developed countries), IgG antibodies target myelin proteins including myelin protein zero (P0), myelin basic protein (MBP), and connexin-32, leading to complement-mediated destruction of myelin sheaths. In motor axonal GBS (AMAN, more common in Asia), antibodies target GM1 and GM3 gangliosides on axonal membranes, causing antibody-mediated complement deposition and axonal destruction; this variant correlates strongly with prior C. jejuni infection with serotypes expressing lipopolysaccharides with GM1-like epitopes.

• Complement activation and inflammation: Following antibody binding to myelin or axonal antigens, the classical complement cascade is activated, generating C3b and C5a. Membrane attack complexes (C5b-9) directly perforate myelin lamellae and axonal membranes. C5a acts as a potent chemotactic factor, recruiting macrophages, neutrophils, and T cells to affected nerve roots and peripheral nerves. The resultant perivascular inflammation and myelin stripping by macrophages produce demyelination with relative preservation of axons (in AIDP). In AMAN, the antibody-mediated complement attack directly targets unmyelinated axons at nodes of Ranvier and axon-Schwann cell junctions, causing axonal degeneration that may be irreversible if severe and prolonged.

• Blood-nerve barrier disruption: The inflammatory cascade increases vascular permeability within the blood-nerve barrier of nerve roots and proximal peripheral nerves, allowing entry of pathogenic antibodies and complement proteins that would normally be excluded. This process is mediated by upregulation of adhesion molecules (ICAM-1, selectins) on endothelial cells and infiltrating leukocytes, and increased production of pro-inflammatory cytokines (TNF-α, IL-6, IL-1β) by macrophages and activated T cells. The result is progressive inflammation and demyelination that spreads proximally from distal nerve segments.

• Conduction block and axonal loss: In demyelinating GBS, loss of myelin over nerve internodes causes demyelination with intact axons. Demyelinated segments exhibit conduction block—failure of action potential propagation—because voltage-gated sodium channels are normally concentrated at nodes of Ranvier under the myelin sheath. Without myelin insulation and with low nodal density on denuded internodes, regenerative current is insufficient to trigger action potentials distally. This causes paralysis despite anatomically intact axons and is reversible with remyelination, explaining the typical recovery phase. In axonal variants, direct axonal destruction leads to Wallerian degeneration distal to the injury site and neuronal cell body responses (chromatolysis), causing more permanent loss of motor units and slower recovery.

• T cell involvement and adaptive immunity: CD8+ T cells infiltrate nerve roots and contribute to demyelination through perforin-mediated and Fas-ligand-mediated killing of myelin-producing Schwann cells. The predisposition to GBS may involve HLA associations (particularly HLA-B35 in some populations) that influence presentation of cross-reactive peptides to T cells. Additionally, molecular mimicry may activate autoreactive T cells and B cells that were incompletely eliminated during negative selection, with the preceding infection providing the "danger signal" and antigenic stimulus necessary to breach regulatory T cell (Treg)-mediated tolerance.

• Pathophysiological basis of clinical manifestations: The ascending paralysis pattern reflects the distribution of inflammation, which begins in distal nerve roots and proximal peripheral nerves (hence distal weakness first) and progresses proximally. Areflexia occurs because the reflex arc involves sensory and motor nerves; demyelination of either component blocks the reflex. The predilection for proximal muscles and respiratory muscles in severe cases reflects the larger diameter of proximal nerve roots and the concentration of inflammatory infiltrates in proximal segments. Autonomic symptoms (tachycardia, hypertension, arrhythmias, urinary retention) result from inflammatory involvement of autonomic nerve fibers, particularly in nerve roots.

• Antecedent gastrointestinal infections: Campylobacter jejuni is the most commonly identified pathogenic trigger, found in 20-40% of GBS cases, particularly in AMAN variants. C. jejuni serotypes (especially O:19) express lipopolysaccharides with GM1-like epitopes that are highly cross-reactive with human gangliosides; patients with serologically confirmed C. jejuni infection followed by GBS have markedly elevated titers of anti-GM1 IgG antibodies. Other bacterial triggers include Salmonella, Shigella, and Yersinia species. Rotavirus and enteroviruses have been implicated in some cases, though the epidemiological evidence is less robust than for C. jejuni.

• Antecedent respiratory infections: Cytomegalovirus (CMV) is a major respiratory pathogen preceding GBS, particularly noted in young adults; anti-CMV IgM seropositivity is found in approximately 10-15% of GBS patients at disease onset. Epstein-Barr virus (EBV), influenza virus, and other respiratory viruses have been documented as triggers, though their relative frequency varies geographically and seasonally.

• Post-vaccination GBS: Vaccines carry a documented, albeit rare, risk of precipitating GBS, likely through molecular mimicry or adjuvant-induced immune activation. The 1976 swine flu vaccine was associated with a notably increased risk (approximately 1 case per 100,000 vaccinees), prompting intensive safety monitoring of subsequent influenza vaccines. More recently, COVID-19 mRNA vaccines (Pfizer-BioNTech, Moderna) and adenovirus-vectored vaccines (AstraZeneca, J&J) have been rarely associated with GBS, though the absolute risk is very low (approximately 1-2 cases per million vaccinations). The temporal relationship is typically 7-42 days post-vaccination. From a risk-benefit perspective, the risk of severe infection-related complications far exceeds vaccine-related GBS risk, but informed consent discussions should acknowledge this potential.

• Surgical procedures and trauma: Physical trauma, elective surgery, and anesthesia have been documented as precipitants, though the mechanism is unclear. Proposed mechanisms include enhanced immune activation from surgical stress or direct nerve trauma.

• Malignancy: Lymphoproliferative malignancies (Hodgkin lymphoma, non-Hodgkin lymphoma) occur with increased frequency in GBS patients, and paraneoplastic GBS variants exist. Malignancy-associated GBS may have distinct antibody profiles targeting tumor-expressed antigens with cross-reactive epitopes.

• HIV infection: Patients with advanced HIV (CD4 count <200) have an increased incidence of GBS, possibly related to concurrent opportunistic infections, impaired immune regulation, or direct effects of HIV on peripheral nerves.

• Idiopathic cases: Approximately 30-40% of GBS cases have no identifiable preceding event. These may represent occult infections not detected by standard serologic testing or may involve triggers yet to be identified.

• Geographic and seasonal variations: The prevalence of specific triggers varies significantly. In developed Western countries, viral infections and vaccinations are more common triggers; in developing countries and parts of Asia, C. jejuni gastroenteritis is more prevalent, correlating with higher rates of AMAN variants.

• Ascending paralysis (classic motor pattern): Paralysis characteristically begins distally in the lower extremities and progresses proximally over hours to days (typically reaching maximum deficit within 2 weeks). Patients initially note bilateral foot weakness, difficulty walking, or inability to rise from sitting. Weakness then involves the thighs, gluteal muscles, and abdominal muscles, with eventual involvement of proximal upper extremities, shoulders, and neck muscles. The pattern is typically symmetric (unlike stroke), distinguishing GBS from central causes. Weakness is flaccid in nature, not spastic. The legs are invariably affected before upper extremities in classic GBS, though all four limbs may become paralyzed in severe cases. Weakness often progresses to requiring mechanical ventilation as intercostal and diaphragmatic muscles become involved.

• Areflexia and hyporeflexia: Loss of deep tendon reflexes is a cardinal and nearly pathognomonic feature of GBS, present in >90% of cases at peak disease. Reflexes typically disappear in the order of disease progression (ankle reflexes first, then knee reflexes, then upper extremity reflexes). The early combination of ascending paralysis with areflexia is highly suggestive of GBS and distinguishes it from other causes of acute paralysis (e.g., transverse myelitis, where reflexes are often preserved or hyperactive). The physiological basis is that conduction block or demyelination of either afferent sensory nerves or efferent motor nerves in the reflex arc prevents reflex completion.

• Sensory symptoms and signs: Although GBS is primarily a motor syndrome, patients often report paresthesias (tingling, pins-and-needles sensations) in fingers and toes, which typically precede motor weakness. These are sensory nerve-irritation symptoms rather than true motor symptoms. On formal sensory examination, objective sensory deficits are mild or absent in classic AIDP, though they may be more prominent in some patients. Sensory examination findings include mild impairment of vibration and proprioception in a distal, symmetric distribution proportionate to motor involvement. The relative preservation of sensory examination despite sensory symptoms is a helpful clinical pearl distinguishing GBS from other polyneuropathies.

• Cranial nerve involvement: Occurs in 40-50% of GBS cases and adds significant morbidity. Facial nerve involvement (CN VII) is most common, manifesting as bilateral facial weakness (often symmetric or near-symmetric). Bulbar involvement (CN IX, X) causes dysarthria, dysphagia, and nasal regurgitation, creating risk for aspiration. Oculomotor nerve involvement (CN III, IV, VI) causes diplopia and ophthalmoplegia (particularly prominent in the Miller Fisher syndrome variant). Acoustic nerve involvement (CN VIII) can cause hearing loss. The development of cranial nerve involvement, particularly bilateral facial weakness, portends more severe disease and higher likelihood of requiring mechanical ventilation.

• Autonomic dysfunction: Seen in 60-70% of patients, manifesting with variable severity. Symptoms include tachycardia, hypertension, arrhythmias (particularly atrial fibrillation, bradycardia, and conduction abnormalities), fluctuating blood pressure, urinary retention (requiring catheterization in ~5% of patients), and hyperhidrosis. Severe autonomic instability can lead to sudden cardiac death and contributes to GBS mortality. The mechanism involves inflammation of autonomic nerve fibers in nerve roots and proximal segments. Autonomic instability typically appears in patients with severe motor involvement.

• Pain syndromes: Muscle pain, particularly in the back and proximal lower extremities, occurs in 40-50% of patients and may precede motor weakness. The character is often described as deep, aching pain in muscles, distinct from the neuropathic paresthesias. Pain can be severe and distressing, often necessitating opioid analgesia. The mechanism likely involves inflammatory neuropathy and possibly irritation of nerve roots.

• Ventilatory involvement and respiratory failure: Develops in 20-30% of patients and is the most life-threatening manifestation. Weakness of intercostal muscles (innervated by thoracic nerve roots) and diaphragm (innervated by C3-C5 phrenic nerve) leads to progressively impaired respiratory mechanics. Patients develop dyspnea, tachypnea, accessory muscle use, orthopnea, and ultimately hypoxemia and hypercapnia. Mechanical ventilation becomes necessary when vital capacity falls below 15-20 mL/kg (approximately 1-1.2 L in adults), or earlier if there is rapid deterioration or inability to protect the airway due to bulbar involvement. The need for mechanical ventilation correlates with severe disease and has major prognostic implications.

• Miller Fisher Syndrome (MFS) variant: Presents with the classic triad of ophthalmoplegia, ataxia, and areflexia, without significant motor weakness of limbs (at least initially). Represents 5% of GBS cases in Western countries but up to 20% in Asia. Ophthalmoplegia is often bilateral and complete, causing profound diplopia and impaired visual tracking. Ataxia is prominent and may exceed the degree of limb weakness. Most patients with MFS eventually develop some limb weakness, blurring the distinction with classic AIDP. MFS typically has better prognosis than classic GBS, with lower rates of mechanical ventilation. The antibody profile in MFS often includes anti-GQ1b IgG antibodies (found in >90% of MFS cases, compared to <5% of classic GBS), which likely target gangliosides concentrated in oculomotor nerves.

• Atypical variants: AMAN (acute motor axonal neuropathy) presents identically to classic AIDP clinically but represents primary axonal injury rather than demyelination; distinguished only by electrodiagnostic testing. AMSAN (acute motor-sensory axonal neuropathy) includes prominent sensory deficits on examination. Pharyngeal-cervical-brachial variant affects upper extremities and bulbar muscles preferentially. Pure autonomic GBS presents with isolated autonomic dysfunction without motor paralysis or sensory symptoms.

• Temporal pattern and disease course: Motor weakness typically develops over 2-4 weeks (range, hours to weeks), with peak deficit reached by definition within 4 weeks (diagnostic criterion). A plateau phase follows, lasting days to weeks, during which disease neither progresses nor improves. The recovery phase begins spontaneously, with gradual improvement over weeks to months; most patients recover substantially within 3-6 months, though complete recovery may take longer. The biphasic course (progression, plateau, recovery) is characteristic of GBS and can be diagnostically helpful when the temporal pattern is clear.

• Clinical diagnostic criteria (Asbury and Cornblath): The Brighton Collaboration case definitions provide standardized diagnostic criteria stratified by certainty level. Probable GBS requires: (1) progressive motor weakness of more than one limb, beginning with leg weakness that is relatively symmetric, (2) areflexia or hyporeflexia (or marked delay in reflexes), and (3) time from onset to nadir of 12 hours to 28 days. Possible GBS has less stringent criteria if one or two features are absent. These clinical criteria alone are sufficient to initiate treatment while awaiting confirmation,

Immediate stabilisation (before any immunotherapy)

• Serial respiratory mechanics: bedside forced vital capacity, negative inspiratory force, and single-breath count every few hours during the progressive phase. The 20/30/40 rule (VC <20 mL/kg, maximal inspiratory pressure weaker than −30 cm H₂O, maximal expiratory pressure <40 cm H₂O) prompts elective intubation. Neuromuscular respiratory failure produces normal oxygen saturation until abrupt collapse, so do not wait for hypoxemia or a hypercapnic blood gas.
• Continuous cardiac telemetry for dysautonomia; anticipate bradyarrhythmia or asystole with vagal stimuli such as tracheal suctioning.
• Supportive care: pharmacologic VTE prophylaxis with low-molecular-weight heparin (e.g., enoxaparin) in non-ambulatory patients, aspiration precautions with bulbar weakness, bowel/bladder care, and neuropathic pain control with a gabapentinoid (gabapentin) rather than escalating opioids alone.

First-line immunotherapy — start early, do not await confirmatory testing

• Intravenous immunoglobulin (IVIG): 0.4 g/kg/day for 5 days. Neutralises pathogenic anti-ganglioside antibodies, blocks Fc receptors, and inhibits complement deposition. Screen for IgA deficiency (risk of anaphylaxis) and assess renal function and thrombotic risk.
• Plasma exchange (PLEX): roughly five exchanges over 1–2 weeks; removes circulating autoantibodies and complement.
• The American Academy of Neurology evidence-based reviews conclude IVIG and PLEX are equally effective when begun within about 2–4 weeks of onset (PLEX best within 2 weeks), and that sequential PLEX followed by IVIG confers no added benefit. Choose based on availability, venous access, and hemodynamic stability. Treat any patient unable to walk unaided.

Escalation

• Treatment-related fluctuation (deterioration after initial improvement) is generally re-treated with a second IVIG course. Complement inhibitors such as eculizumab remain investigational.
• Prolonged mechanical ventilation warrants early tracheostomy planning and intensive rehabilitation, which drives long-term functional outcome.

Contraindicated / avoid

• Corticosteroids: ineffective as monotherapy and not recommended by the AAN — a favourite distractor.
• Succinylcholine: upregulated extrajunctional acetylcholine receptors cause life-threatening hyperkalemia; use a non-depolarising agent.

Disease-related — emergencies

• Neuromuscular respiratory failure (emergency): intercostal and diaphragmatic denervation. Signalled by a falling vital capacity, single-breath count under ~20, orthopnea, paradoxical abdominal motion, or staccato speech — not by desaturation, which occurs late.
• Autonomic instability (emergency): inflammation of autonomic fibres in nerve roots causes labile hypertension alternating with hypotension, tachyarrhythmias, and vagally mediated bradycardia or asystole, classically triggered by tracheal suctioning. Signalled by wide beat-to-beat blood pressure swings on telemetry; a cause of sudden death.
• Aspiration pneumonia: bulbar (CN IX/X) weakness with impaired cough; signalled by wet voice, nasal regurgitation, or a failed swallow evaluation.
• Ileus and urinary retention: autonomic involvement; distended bladder or absent bowel sounds.
• SIADH: hyponatremia with concentrated urine, most often in ventilated patients.
• Venous thromboembolism: immobility-driven stasis; unexplained tachycardia or hypoxemia should raise concern for pulmonary embolism.
• Residual disability: axonal loss (AMAN/AMSAN) with Wallerian degeneration predicts incomplete recovery, persistent fatigue, and chronic neuropathic pain.
• Evolution to CIDP: deterioration continuing or recurring beyond about 8 weeks reclassifies the illness as chronic inflammatory demyelinating polyradiculoneuropathy.

Treatment-related

• IVIG: hyperviscosity-associated arterial and venous thrombosis (stroke, MI, DVT); acute kidney injury (osmotic tubular injury, historically with sucrose-stabilised products); aseptic meningitis with headache and neck stiffness; hemolytic anemia from isoagglutinins; anaphylaxis in IgA-deficient patients.
• Plasma exchange: citrate-induced hypocalcemia — perioral paresthesias, Chvostek sign, QT prolongation; hypotension from volume shifts; coagulation factor and fibrinogen depletion with bleeding; central catheter infection and pneumothorax.
• Immobility/ICU care: pressure ulcers, ICU-acquired weakness, and corneal exposure keratopathy with bilateral facial palsy.

• The buzzword pair: ascending symmetric flaccid weakness with areflexia plus albuminocytologic dissociation on CSF (high protein, normal cell count). A CSF pleocytosis should redirect you toward HIV seroconversion, Lyme polyradiculitis, sarcoidosis, or CMV radiculitis.
• Single best next step in a progressing patient is bedside spirometry, not an arterial blood gas, not pulse oximetry, and not MRI. Serial forced vital capacity detects impending neuromuscular respiratory failure while gas exchange is still normal.
• Do not delay immunotherapy for confirmatory testing. CSF protein is often normal in the first week and nerve conduction studies may lag; treat on clinical grounds per the American Academy of Neurology approach.
• The association examiners test: Campylobacter jejuni gastroenteritis 1–3 weeks earlier → anti-GM1 antibodies → axonal (AMAN) GBS. The other testable antibody is anti-GQ1b in Miller Fisher syndrome (ophthalmoplegia, ataxia, areflexia).
• Corticosteroids are the classic distractor — ineffective in GBS, in contrast to their central role in CIDP and multiple sclerosis relapses. Likewise, combining IVIG with plasma exchange adds nothing; pick one.
• Never give succinylcholine if intubation is needed: denervation-induced extrajunctional acetylcholine receptors cause massive hyperkalemia and cardiac arrest.
• Suctioning-induced bradyasystole is the dysautonomia vignette; atropine at the bedside and telemetry are the expected answers.
• Distinguish the mimics: botulism is descending with pupillary involvement and preserved reflexes early; transverse myelitis gives a sensory level with bowel/bladder dysfunction and later hyperreflexia; tick paralysis is ascending and areflexic but resolves after removing the tick — do a full scalp and skin exam; hypokalemic periodic paralysis has a low serum potassium and no sensory symptoms.
• Time defines the disease: nadir within 4 weeks is GBS; progression or relapse beyond ~8 weeks is CIDP.