Guillain-Barré Syndrome

Guillain-Barré syndrome (GBS) is an acute, immune-mediated polyneuropathy and the most frequent cause of subacute neuromuscular weakness in North America.^[1] In most cases, the immune response to a preceding infection cross-reacts with peripheral nerve components through molecular mimicry: antibodies raised against infectious antigens — most classically the lipooligosaccharides of Campylobacter jejuni — structurally resemble gangliosides that reside at high density in the axolemma of peripheral nerves, triggering complement activation, macrophage infiltration, and inflammatory edema of the nerve roots and peripheral nerves.^[2] The result is an ascending immune-mediated polyneuropathy — weakness beginning in the legs and progressing upward — that can be predominantly demyelinating (acute inflammatory demyelinating polyradiculoneuropathy, AIDP, the most common pattern in North America and Europe) or predominantly axonal (acute motor axonal neuropathy, AMAN, or acute motor sensory axonal neuropathy, AMSAN).^[2]

GBS is fundamentally an emergency-recognition condition: autonomic dysfunction and respiratory muscle weakness can progress — sometimes rapidly — to require ICU-level monitoring and mechanical ventilation, and this evolving trajectory, more than any single finding at presentation, is why early recognition and close monitoring for respiratory decline is the central safety message of this chapter.^[1] Two disease-modifying therapies — intravenous immunoglobulin (IVIG) and plasma exchange (plasmapheresis) — are equally effective at hastening recovery; corticosteroids, despite being immunosuppressive, are specifically not effective in GBS and are not recommended, a genuine exception to how many other autoimmune neurologic conditions are treated.^[3][4]

Epidemiology

The median incidence of GBS is about 1 per 100,000 person-years, with a roughly 20% increase in the average rate for every 10-year increase in age, and higher rates in males.^[1] Worldwide estimates run somewhat higher, at 1 to 4 per 100,000 population annually; GBS causes respiratory failure requiring ventilation in about 25% of patients, with associated mortality of 4-15% and persistent disability in about 20%.^[3]

Antecedent triggers — infection, and the honest vaccine-safety context

A majority of patients report an antecedent infectious illness, typically respiratory or gastrointestinal, in the 1 to 3 weeks (occasionally longer) before weakness begins.^[2] Campylobacter jejuni gastroenteritis is the most classically associated trigger, but cytomegalovirus, hepatitis E virus, and Zika virus, among other pathogens, have each been linked to GBS in case-control studies.^[2][1]

GBS can also very rarely follow vaccination, and this deserves honest, proportionate treatment rather than either dismissal or alarm. A large retrospective cohort study published in 2013 found no overall increased risk of GBS after vaccination.^[1] At the same time, Canadian vaccine safety surveillance treats GBS as a genuine adverse event of special interest and classifies reported cases by diagnostic certainty using the internationally standardized Brighton Collaboration case definition.^[5] During the COVID-19 vaccination program, the Public Health Agency of Canada and Health Canada identified and actively monitored a specific, real safety signal: as of July 2021, Canada had received 85 reports of GBS meeting Brighton diagnostic-certainty criteria following COVID-19 vaccination — 32 after AstraZeneca Vaxzevria/COVISHIELD, 34 after Pfizer-BioNTech Comirnaty, and 19 after Moderna Spikevax — with the AstraZeneca-associated reports (23 after a first dose, onset 6 hours to 25 days later, median age 55) occurring at a rate the report described as higher than would normally be expected in the general population, prompting formal signal monitoring as one of three ongoing safety signals at that time.^[5] The clinically useful takeaway for a pharmacist is not to discourage immunization, but to recognize that a genuine, small, product-specific association existed for adenovirus-vector COVID-19 vaccines, and to take any new ascending weakness seriously regardless of a recent vaccination, infection, both, or neither.

Classic presentation

In primary care, patients most commonly present first with acroparesthesias, followed by subacute (developing over less than 4 weeks), symmetric, flaccid weakness with hyporeflexia; weakness usually begins in the lower extremities and ascends.^[1] Sensory symptoms are variable — many patients have paresthesias or mild sensory loss, though predominantly motor presentations occur, particularly in the axonal subtypes.^[2] As weakness progresses, watch specifically for the two features that define this chapter's central safety message: autonomic dysfunction (labile blood pressure, arrhythmia, ileus, urinary retention) and respiratory muscle weakness, either of which can progress — sometimes over hours — to require ICU-level monitoring and mechanical ventilation; nearly one-third of patients with GBS require mechanical ventilation.^[1]

Subtypes and variants

^[2]

• Antecedent Campylobacter jejuni gastroenteritis — the most classically associated and most extensively studied trigger, and the trigger most strongly linked to the axonal (AMAN) subtype.^[2]
• Other antecedent infections, including cytomegalovirus, hepatitis E virus, and Zika virus.^[2]
• Recent vaccination, very rarely — see Recognize the Condition for the specific, honestly presented Canadian surveillance data; the great majority of GBS has no vaccine association at all.^[1][5]
• Older age — each 10-year increase in age raises the average GBS rate by about 20%.^[1]
• Male sex — a modestly higher incidence than in women.^[1]
• No preceding trigger is identified in a meaningful minority of patients — a clear antecedent event is not required to consider the diagnosis.

GBS is primarily a clinical diagnosis

Diagnosis rests on the history and examination pattern described in Recognize the Condition — subacute, ascending, symmetric weakness with hyporeflexia — supported by cerebrospinal fluid (CSF) analysis and nerve conduction studies; it should not wait for either test to be completed before initiating monitoring and, where indicated, treatment.^[1]

CSF analysis — collect it, and know what it should (and should not) show

Collect CSF on presentation, both to support the diagnosis and to exclude infectious mimics.^[1] The classic finding is albuminocytologic dissociation — an elevated CSF protein with a normal white blood cell count — present in 50-70% of GBS cases in the first week of illness, so a normal early CSF protein does not exclude the diagnosis.^[1] Pleocytosis is a red flag against GBS, not a supportive finding, and should prompt evaluation for an infectious mimic such as Lyme disease, HIV, enterovirus, or West Nile virus instead.^[1]

Nerve conduction studies and electromyography

Electrodiagnostic testing supports subtyping into a demyelinating pattern (AIDP) or an axonal pattern (AMAN/AMSAN), though testing can be normal early in the illness and should not be used to exclude the diagnosis when the clinical picture is convincing.^[2] The distinction matters for counseling: an axonal subtype, or unexcitable nerves on early testing, predicts a longer course to mechanical-ventilation weaning and a slower recovery.^[2]

Differentiating GBS from its principal mimics

^[1][2]

Predicting the need for mechanical ventilation — the EGRIS score

The Erasmus GBS Respiratory Insufficiency Score (EGRIS) combines three variables available at hospital admission — the number of days between the onset of weakness and admission, the presence of facial and/or bulbar weakness, and the total Medical Research Council (MRC) sum score for muscle strength — into a single score used to estimate the probability of needing mechanical ventilation within the first week.^[7] It is presented here as a teaching reference to frame clinical urgency, not as a live calculator or a substitute for the serial bedside respiratory monitoring described in Non-Pharmacologic Management.

^[2]

• Halt further immune-mediated nerve injury and hasten recovery with disease-modifying immunotherapy — IVIG or plasma exchange — started as early as possible in an appropriately selected patient.
• Anticipate and prevent respiratory crisis through proactive serial monitoring rather than reactive management after overt failure.
• Recognize and manage autonomic dysfunction safely, including cardiac monitoring and cautious, conservative treatment of blood pressure lability and arrhythmia.
• Prevent venous thromboembolism during the period of immobility.
• Treat neuropathic and nociceptive pain effectively — pain is common, can be severe, and is under-recognized.
• Support the patient and family through a genuinely variable, often prolonged recovery course with realistic counseling and proactive rehabilitation referral.
• Avoid ineffective or harmful therapy — most importantly, corticosteroids and combined or sequential IVIG-plus-plasma-exchange regimens, neither of which adds benefit.

IVIG dosing

Total dose 2 g/kg IV, given as 0.4 g/kg once daily for 5 consecutive days.^[2] Screen for known IgA deficiency where feasible before the first infusion (see Special Populations), and infuse at the slowest rate consistent with the product monograph, particularly in patients with renal impairment, diabetes, or volume depletion.

Plasma exchange protocol

Typically five exchanges, together removing a total of about 200-250 mL of plasma per kg body weight, performed via a large-bore central catheter over roughly 1-2 weeks.^[2] Plasma exchange carries a somewhat higher risk of treatment-related side effects than IVIG and is more difficult to administer, largely reflecting the vascular-access and apheresis-resource requirements rather than any lesser efficacy.^[3]

Corticosteroids are NOT effective in GBS — a genuine, important exception

• Admit every patient with confirmed or strongly suspected GBS for monitoring, regardless of how mild weakness appears at presentation — the course is genuinely unpredictable early on.^[1]
• Serial respiratory monitoring: measure vital capacity (VC), maximal inspiratory pressure (MIP, also called negative inspiratory force/NIF), and maximal expiratory pressure (MEP) every 4-6 hours, more frequently if any parameter is declining or the patient is symptomatic. The "20/30/40 rule" — VC under 20 mL/kg, MIP less negative than 30 cm H₂O, or MEP under 40 cm H₂O, or a decline of more than 30% in any of these — flags patients at high risk of needing mechanical ventilation and should prompt elective intubation rather than waiting for a respiratory crisis.^[6]
• Continuous cardiac telemetry and regular blood pressure monitoring for autonomic dysfunction; treat labile blood pressure and arrhythmia conservatively and favour short-acting agents given the unpredictable, sometimes exaggerated autonomic response in GBS.^[2]
• Venous thromboembolism prophylaxis (mechanical plus pharmacologic — see Drug Tables) for every non-ambulatory patient, continued until independent ambulation resumes; deep vein thrombosis is a recognized complication of the prolonged immobility in GBS requiring standard-practice preventive measures.^[2]
• Proactive nutrition support (enteral if bulbar weakness or intubation limits safe oral intake) alongside bowel and bladder monitoring for autonomic involvement.^[2]
• Arrange physical, occupational, and respiratory therapy early and proactively rather than only once weaning begins — recovery is genuinely protracted for many patients.
• Encourage mobilization as early as safely possible alongside pharmacologic pain management — non-pharmacologic measures alone are not sufficient for the neuropathic pain that affects at least a third of patients at 1 year.^[2]
• Screen for and address the psychological impact of a prolonged ICU stay, mechanical ventilation, and an unpredictable recovery trajectory — easy to overlook once the acute paralysis has resolved.

Pregnancy

GBS in pregnancy is treated the same as in a non-pregnant patient — IVIG or plasma exchange remain the disease-modifying options of choice. Involve obstetrics or maternal-fetal medicine early for shared monitoring, particularly around the airway/respiratory-monitoring plan and delivery timing.

Breastfeeding

IVIG and plasma exchange are both compatible with breastfeeding. Gabapentin and pregabalin are generally considered compatible; confirm specifics against each drug's own Drug Database entry before use.

Pediatrics

GBS in children generally follows a similar clinical course to adults, though it is often somewhat milder. Both IVIG and plasma exchange are reasonable treatment options for children with severe GBS, based on evidence extrapolated from adult trials.^[3]

Older adults

Age is itself a risk factor — the average GBS rate rises by about 20% for every decade of age.^[1] Older adults are more likely to have a slower, less complete recovery; maintain a lower threshold for proactive respiratory and cardiac monitoring in this group, and dose-adjust gabapentin, pregabalin, and the LMWHs for age-related renal decline.

Renal impairment

Use IVIG cautiously in renal impairment — it carries a genuine risk of IVIG-associated acute kidney injury, particularly with sucrose-stabilized formulations and in patients with pre-existing renal impairment, diabetes, or volume depletion; favour a non-sucrose formulation where available, ensure adequate hydration, and infuse at the slowest rate consistent with the product monograph. Plasma exchange avoids this specific risk and may be preferred in significant renal impairment. Adjust enoxaparin and dalteparin doses for reduced renal function; unfractionated heparin (no renal clearance dependence) is a reasonable VTE-prophylaxis alternative in severe impairment. Adjust gabapentin and pregabalin doses for reduced renal function.

Hepatic impairment

No specific IVIG or plasma exchange dose adjustment is required for hepatic impairment. Use carbamazepine cautiously given its hepatotoxicity risk, and reduce the total daily acetaminophen dose in significant hepatic impairment.

Miller Fisher syndrome and other variants

Miller Fisher syndrome — the triad of ophthalmoplegia, areflexia, and ataxia — accounts for roughly 5-25% of the GBS spectrum and tends to follow a relatively mild course, with many patients recovering without disease-modifying treatment; however, a subgroup goes on to develop limb weakness indistinguishable from classic GBS, so the same monitoring principles apply until the course is clear.^[2]

IgA-deficient patients

Screen for known IgA deficiency before IVIG where feasible — the anaphylaxis risk described in the Drug Tables is specific to this population; plasma exchange is a reasonable alternative if IgA deficiency is known or strongly suspected.

Continue serial VC/MIP/MEP monitoring and cardiac telemetry through the period of disease progression and the early plateau, not only during the initial admission.^[6]

• Track the expected trajectory: clinical nadir typically occurs at 2-4 weeks, after which recovery begins; about 83% of patients can walk independently by 6 months, though persistent leg weakness, pain, and fatigue are common even after that point.^[1]
• Up to two-thirds of GBS deaths occur during the recovery phase, from cardiovascular or respiratory dysfunction, particularly in patients recently discharged from ICU-level care — do not relax monitoring intensity simply because the patient has left the ICU.^[2]
• Watch specifically in the weeks after apparent stabilization or initial improvement for a treatment-related fluctuation — new worsening after an initial response — which is a recognized pattern distinct from a chronic inflammatory demyelinating polyneuropathy misdiagnosis (see Treatment Failure/Next Step).^[2]
• Arrange or confirm ongoing physical, occupational, and respiratory therapy at every follow-up, and reassess neuropathic pain control (see Pharmacologic Treatment Options) rather than assuming it resolves on its own.
• Complete medication reconciliation, including VTE-prophylaxis duration (stop once ambulation is independent) and any neuropathic pain agent taper plan.

1. Continued progression of weakness or respiratory decline during or shortly after a full course of IVIG or plasma exchange: this does not necessarily mean treatment failed — the natural history of GBS can include ongoing progression for up to 4 weeks from onset — but it does mean escalating monitoring and involving neurology/critical care, not simply repeating the same treatment reflexively.^[2]
2. Genuine treatment-related fluctuation — new deterioration after an initial clear response: consider a second course of the same disease-modifying therapy, or switching to the alternative (IVIG after plasma exchange, or vice versa), in consultation with neurology.^[2]
3. A relapsing-remitting course, or deterioration well beyond the typical GBS progression window: reconsider the diagnosis — this pattern is more consistent with chronic inflammatory demyelinating polyneuropathy (CIDP) than GBS, and management differs meaningfully, including a role for corticosteroids in CIDP that does not apply to GBS.^[2]
4. Autonomic instability not controlled with conservative measures: escalate to critical care for closer titration of short-acting agents rather than reaching for longer-acting antihypertensives or antiarrhythmics empirically.^[2]
5. Respiratory parameters crossing the 20/30/40 threshold at any point, including overnight or between scheduled measurements: proceed to elective intubation on that finding alone — do not wait for a repeat measurement or for overt distress.^[6]
6. Diagnostic uncertainty at any stage — an atypical pattern, fever, true CSF pleocytosis, or a descending rather than ascending course: reconsider infectious or toxin-mediated mimics (see Assessment & Diagnosis) rather than continuing to treat empirically as GBS.

• Waiting for CSF or electrodiagnostic confirmation before admitting for monitoring or before starting disease-modifying therapy in a clinically convincing, progressing presentation.
• Using corticosteroids for GBS, alone or added to IVIG — Level A evidence shows no benefit, unlike in many other autoimmune neurologic conditions.^[3][4]
• Combining or sequencing IVIG and plasma exchange in the hope of an additive effect — trial evidence shows no benefit over either alone.^[3]
• Reassuring a patient with early, mild ascending weakness and discharging home without arranging monitoring — the course is genuinely unpredictable, and respiratory/autonomic decline can develop over hours.
• Waiting for overt respiratory distress rather than intubating electively once the 20/30/40 threshold is crossed.^[6]
• Assuming CSF pleocytosis is consistent with GBS — it is a red flag for an infectious mimic instead.^[1]
• Confusing GBS's ascending pattern with botulism's descending, cranial-nerve-first pattern, or missing the sensory involvement and CSF changes that point toward GBS rather than botulism.
• Discouraging routine immunization broadly because of the rare, product-specific vaccine-associated GBS signal — the appropriate response is proportionate awareness and prompt reporting, not blanket vaccine avoidance.^[1][5]
• Under-treating neuropathic pain, or reaching for carbamazepine first, when gabapentin has stronger trial evidence and less sedation in this specific population.^[8]
• Stopping VTE prophylaxis prematurely, or continuing it well past the point of independent ambulation without reassessing the ongoing indication.
• Attributing new, delayed deterioration to a GBS relapse without reconsidering CIDP.^[2]

How to use this table: Doses are adult doses and require patient-specific confirmation (renal/hepatic function, weight, allergy history). Pediatric dosing is weight-based per the current product monograph unless stated. Drug pricing is intentionally omitted. Select any drug name to open its complete Pharmasist Drug Database page.

Disease-Modifying Immunotherapy

Equally effective (Level A) — choose based on availability, contraindications, and local expertise; do not combine or give sequentially.

Not Recommended — Corticosteroids

Level A evidence against benefit in GBS, at any severity, alone or added to IVIG — do not use, despite corticosteroids being foundational therapy in many other autoimmune neurologic conditions.

Neuropathic and Nociceptive Pain Management

Neuropathic pain affects at least a third of patients at 1 year and is frequently under-treated — assess and manage it as actively as the disease-modifying therapy itself.

VTE Prophylaxis (Non-Ambulatory Patients)

Continue mechanical plus pharmacologic prophylaxis until the patient regains independent ambulation.