TRIGGER 1: 70-Year-Old Woman - Sudden Aphasia + Right UL Weakness with Complete Recovery

1. Neuroanatomical Correlation and Vascular Territory

The Two Deficits and Their Anatomical Substrates

The Unifying Vascular Territory

2. TIA vs. Ischemic Stroke - Definition, Presentation, Pathophysiology

Definition of TIA

Clinical Comparison

Pathophysiology Comparison

1. Large-artery atherosclerosis - plaque rupture or ulceration in the carotid or intracranial arteries causes thromboembolism. The thrombus either partially or transiently occludes a vessel (TIA) or causes sustained occlusion with infarction (stroke).
2. Cardioembolism - clots from AF, valvular disease, or LV thrombus embolize to cerebral arteries. A small embolus may lyse spontaneously (TIA); a large one causes persistent occlusion (stroke).
3. Small-vessel (lacunar) disease - lipohyalinosis of perforating arteries from chronic hypertension.
4. Hemodynamic - systemic hypoperfusion through a severely stenotic artery.

• In TIA: ischemia is brief (collateral flow, spontaneous thrombolysis, transient embolus) - the ischemic penumbra recovers before irreversible cell death occurs.
• In ischemic stroke: sustained ischemia (core CBF <10 mL/100g/min) triggers the ischemic cascade - glutamate excitotoxicity, calcium influx, mitochondrial failure, apoptosis, and ultimately infarction. Neurons in the ischemic core die within minutes; the penumbra is at risk for 6-24 hours. - Goldman-Cecil Medicine, Chapter 376

3. Emergency Diagnostic Workup

Neuroimaging (First Priority)

Vascular Imaging

Cardiac Evaluation

Blood Tests

• FBC, coagulation screen (thrombocytosis, hypercoagulable state)
• Fasting lipid profile + HbA1c (modifiable risk factor quantification)
• Blood glucose (hypoglycaemia is a TIA mimic - must exclude immediately)
• Renal function + electrolytes
• ESR/CRP (vasculitis in atypical presentations)
• In younger patients: thrombophilia screen (protein C/S, antithrombin, antiphospholipid antibodies), VDRL

ABCD² Score (Risk Stratification)

4. Acute Management and Long-Term Secondary Prevention

Acute Clinical Approach

• Admit for monitoring (at minimum, urgent TIA clinic if low risk score)
• Aspirin 300 mg loading dose as soon as hemorrhage is excluded on CT
• Dual antiplatelet therapy (aspirin + clopidogrel) for 21 days if ABCD² score ≥4 and no cardioembolic source (POINT and CHANCE trials showed significant reduction in 90-day stroke)
• Blood pressure management: avoid aggressive lowering acutely (may worsen penumbral ischemia); target <140/90 once stabilized
• Blood glucose control
• Urgent neurology referral and stroke unit care

Long-Term Secondary Prevention

Antiplatelet Therapy

• Aspirin (75-325 mg/day), clopidogrel (75 mg/day), or aspirin + sustained-release dipyridamole (25/200 mg twice daily) are established options.
• For non-cardioembolic TIA: single antiplatelet long-term; short-term DAPT for the first 21 days.
• For AF-related TIA: anticoagulation with a direct oral anticoagulant (DOAC) (e.g., apixaban, rivaroxaban) is superior to antiplatelet therapy. The annual stroke risk with untreated AF is 6-10%.

Statin Therapy

• High-intensity statin (atorvastatin 40-80 mg or rosuvastatin 20-40 mg) for all patients with TIA/stroke and atherosclerotic disease, diabetes, or hyperlipidaemia.
• Target LDL <70 mg/dL - reduces recurrent stroke and cardiovascular events by ~20%.
• Stopping a statin after acute ischemic stroke is associated with increased morbidity and mortality.

Blood Pressure Control

• A 10/5 mmHg reduction is associated with ~25% reduction in recurrent stroke risk.
• Target <130/80 mmHg in most patients.
• Preferred agents: ACE inhibitors, ARBs, calcium channel blockers, thiazide diuretics.

Carotid Revascularization

• If symptomatic ipsilateral carotid stenosis 70-99%: carotid endarterectomy (CEA) or carotid artery stenting (CAS) within 2 weeks of TIA (reduces recurrence by ~50%).
• Stenosis 50-69%: benefit present but smaller (~16% relative reduction).
• <50% stenosis: no benefit from revascularization.

Risk Factor Modification

TRIGGER 2: 38-Year-Old Man - Progressive Bilateral Leg Weakness + Tingling Feet (3-4 Day History)

Differential Diagnosis: Acute/Subacute Ascending Symmetrical Motor Weakness + Distal Sensory Symptoms

Tier 1: Most Likely - Must Not Miss

1. Guillain-Barré Syndrome (GBS) - AIDP Variant

• Acute immune-mediated polyradiculoneuropathy, most common cause of acute flaccid paralysis. - Washington Manual, p. 1034
• Classically preceded by a viral illness (CMV, EBV, Campylobacter gastroenteritis) 1-3 weeks before onset; pathogenesis via molecular mimicry generating autoantibodies that attack peripheral myelin (AIDP) or axolemmal gangliosides (axonal variants).
• Key features: Progressive symmetric ascending weakness beginning in the distal legs, distal paresthesias, areflexia or hyporeflexia (hallmark), back/hip pain.
• Bilateral facial weakness in ~50% of patients.
• Autonomic instability (labile BP, tachycardia) in ~60%.
• Respiratory failure requiring intubation in 25-30%.
• Disease progression peaks at 4 weeks (by definition).
• CSF: Cytoalbuminous (albuminocytological) dissociation - elevated protein (>45 mg/dL) with normal/minimal cells (<10 WBC). Note: CSF may be normal in first 1-2 days.
• Nerve conduction studies (NCS/EMG): Demyelinating pattern (prolonged latencies, slow conduction velocities, conduction block, absent F waves/H reflexes).
• The Washington Manual of Medical Therapeutics, p. 1034-1036

2. GBS Subtypes to Recognize

Tier 2: Important Alternatives

3. Chronic Inflammatory Demyelinating Polyneuropathy (CIDP) - Acute Presentation

• Resembles GBS but progresses beyond 8 weeks (relapsing-remitting or chronic progressive).
• May present acutely and be indistinguishable from GBS early on.
• Treatment differs: responds to steroids (unlike GBS), IVIG, plasmapheresis.

4. Acute Spinal Cord Compression / Transverse Myelitis

• Bilateral leg weakness with a sensory level, bladder/bowel dysfunction, and UMN signs (hyperreflexia, upgoing plantars) rather than LMN signs.
• Causes: disc herniation (usually asymmetric), epidural abscess/haematoma, metastatic cord compression, transverse myelitis (inflammatory/demyelinating).
• Red flag features distinguishing from GBS: UMN signs, bladder retention, clear sensory level, back pain with point tenderness.
• MRI spine is mandatory to exclude.

5. Multiple Sclerosis (MS) - Spinal Cord Attack

• Young adults, bilateral limb weakness with sensory symptoms, but typically UMN pattern, and may have prior neurological episodes or other demyelinating lesions on MRI.
• Uhthoff's phenomenon (worsening with heat) may be a clue.

6. West Nile Virus / Enterovirus Acute Flaccid Myelitis

• Anterior horn cell involvement (poliolike); typically asymmetric flaccid weakness with fever, CSF pleocytosis.
• Geography and fever clues distinguish from GBS.

Tier 3: Less Common but Recognised

7. Myasthenia Gravis (MG)

• Neuromuscular junction disorder; usually descending (ocular, bulbar, then limb); fatigability; NOT ascending; sensory symptoms absent.
• Anti-AChR or anti-MuSK antibodies; repetitive nerve stimulation shows decremental response.

8. Tick Paralysis

• Neurotoxin from tick saliva blocks sodium channels → acute ascending flaccid paralysis WITHOUT sensory symptoms (or mild).
• Diagnosis: find and remove the tick → dramatic recovery within hours.
• Key distinguisher: NO sensory paresthesias; tick exposure history.

9. Botulism

• Clostridium botulinum toxin blocks acetylcholine release at NMJ → descending flaccid paralysis (cranial nerves first: diplopia, dysarthria, dysphagia → limbs).
• NOT ascending. Associated with autonomic features (dry mouth, fixed dilated pupils, constipation).

10. Acute Intermittent Porphyria (AIP)

• Episodic acute peripheral neuropathy with abdominal pain, psychiatric symptoms, autonomic dysfunction, and motor weakness.
• Precipitated by fasting, certain drugs, hormonal changes.
• Urine porphobilinogen elevated during attack.

11. Toxic Neuropathies

• Heavy metals (arsenic, lead, thallium), chemotherapy agents, organophosphates.
• History of exposure is key.

12. Hypokalemic/Hyperkalemic Periodic Paralysis

• Episodic flaccid weakness without sensory symptoms; serum K+ is diagnostic.
• May be precipitated by carbohydrate load, exercise, or medications.

13. HIV-Related Polyradiculopathy / Lyme Neuroborreliosis

• In endemic areas or at-risk populations.
• CMV polyradiculopathy in HIV with low CD4 can cause rapidly progressive ascending weakness.

Diagnostic Approach for Trigger 2

1. MRI spine (cervical-thoracic-lumbar) with gadolinium - exclude cord compression or myelitis
2. Lumbar puncture - CSF protein, glucose, cells, oligoclonal bands, cytology
3. Nerve conduction studies (NCS) + EMG - confirm polyradiculoneuropathy vs myelopathy
4. Bedside respiratory monitoring - FVC and NIF (20/30 rule); admit to HDU/ICU if FVC <20 mL/kg or NIF > -30 cmH₂O
5. Electrolytes (K+, Ca²+, Mg²+), blood glucose
6. Anti-ganglioside antibodies (anti-GM1, anti-GQ1b)
7. Antibiotic/antiviral history, tick exposure, travel history
8. In young patients: anti-AChR antibodies, serum porphyrins, HIV serology

• CIDP (acute presentation)
• Paraproteinemic/paraneoplastic polyradiculopathy
• West Nile and polioviruses (fever + CSF pleocytosis + often asymmetric)
• HIV, Lyme disease
• Tick paralysis, botulism
• Myasthenia gravis (MFS variant)
• Periodic paralysis
• Acute intermittent porphyria
• Arsenic, lead toxicity
• Critical illness myopathy
• Functional weakness

Summary Table: Key Differentiators

Trigger 2: 38-Year-Old Man - Progressive Bilateral Leg Weakness (3 days) + Tingling Feet (1 week)

PART 1: Differential Diagnosis

Clinical Localization First

TIER 1 - Leading Diagnosis: Must Confirm or Exclude First

1. Guillain-Barré Syndrome / AIDP (Primary Suspect)

• Bilateral leg weakness progressing over days
• Preceding distal sensory symptoms (tingling feet for 1 week - the sensory prodrome typically precedes motor weakness)
• Areflexia (the invariable hallmark)
• Likely history of an antecedent viral or GI illness 1-3 weeks prior

TIER 2 - Serious Alternatives Requiring Urgent Exclusion

2. Acute Spinal Cord Pathology

3. Chronic Inflammatory Demyelinating Polyneuropathy (CIDP) - Acute Onset

• Clinically indistinguishable from GBS in the first 4-8 weeks.
• If weakness continues to progress beyond 8 weeks or a relapsing-remitting course emerges, CIDP becomes the diagnosis.
• Responds to corticosteroids (unlike GBS), IVIG, and plasmapheresis.
• Associated with paraproteinaemias, lymphoma, HIV. - Robbins & Kumar Basic Pathology, p. 809

4. West Nile Virus / Enteroviral Acute Flaccid Myelitis

• Anterior horn cell (lower motor neuron) destruction → acute flaccid limb weakness
• Usually asymmetric, associated with fever and CSF pleocytosis (distinguishes from GBS's albuminocytological dissociation)
• Seasonal (summer/autumn), geographic exposure

5. Lyme Neuroborreliosis

• In endemic areas, Borrelia burgdorferi can cause polyradiculoneuropathy
• May present with painful ascending weakness, cranial nerve palsies (especially facial nerve)
• Associated with erythema migrans rash history, tick exposure
• CSF shows pleocytosis (differs from GBS)

TIER 3 - Important Diagnoses with Distinctive Features

6. Botulism

• Descending paralysis (cranial nerves first: diplopia, dysarthria, dysphagia → then limbs) - NOT ascending
• Autonomic: dry mouth, fixed dilated pupils, constipation
• Exposure history: canned/preserved foods, wound, infant honey
• No sensory symptoms; NCS shows presynaptic NMJ defect

7. Tick Paralysis

• Neurotoxin (from Dermacentor or Amblyomma ticks) → blocks sodium channels → ascending flaccid paralysis
• No sensory symptoms (a key distinguisher from GBS)
• Rapid resolution within hours of tick removal
• Tick found on scalp or skin folds

8. Myasthenia Gravis (MG)

• NMJ disorder; typically descending and fatigable (worse with sustained activity)
• Ocular involvement (ptosis, diplopia) is often the first sign
• No sensory symptoms
• Anti-AChR or anti-MuSK antibodies; decremental response on repetitive nerve stimulation

9. Acute Intermittent Porphyria (AIP)

• Motor neuropathy precipitated by fasting, alcohol, certain drugs (barbiturates, sulfonamides, hormones), hormonal fluctuations
• Associated with severe colicky abdominal pain, psychiatric symptoms (confusion, psychosis), autonomic dysfunction
• Urine: elevated porphobilinogen (PBG) during attack
• Sensory symptoms may co-exist but motor weakness dominates

10. Hypokalaemic Periodic Paralysis

• Episodes of profound flaccid limb weakness (legs > arms), often triggered by carbohydrate-rich meals, rest after exercise, cold
• No sensory symptoms and normal reflexes between attacks
• Serum K⁺ low during attack; ECG changes
• Secondary causes: thyrotoxicosis (thyrotoxic periodic paralysis in Asian males)

11. Toxic and Metabolic Neuropathies

• Arsenic poisoning: ascending sensorimotor neuropathy with GI symptoms, Mee's lines on nails, alopecia
• Lead neuropathy: predominantly motor (wrist/foot drop), axonal
• Alcohol: distal symmetric sensorimotor neuropathy, chronic
• Chemotherapy agents (taxanes, platinum compounds, vincristine): length-dependent sensorimotor neuropathy

12. Acute Inflammatory Myopathy (Polymyositis/Dermatomyositis)

• Proximal muscle weakness (difficulty climbing stairs, rising from chair), NOT distal or ascending
• No sensory symptoms; reflexes usually preserved
• Elevated CK, myopathic EMG pattern
• Dermatomyositis: skin features (heliotrope rash, Gottron's papules)

13. HIV-Related Neuropathy / CMV Polyradiculopathy

• In HIV with low CD4 (<50 cells/μL): CMV polyradiculopathy causes rapidly progressive ascending weakness with sacral paresthesias, bladder dysfunction
• CSF shows pleocytosis + CMV PCR positive

Summary Differential Table

PART 2: Pathophysiology of GBS / AIDP - Immune Mechanisms and Clinical Progression

Overview

Step 1: The Antigenic Trigger - Antecedent Infection

Step 2: Immune Mechanism - Molecular Mimicry

• C. jejuni lipooligosaccharides (LOS) share ganglioside-like epitopes with peripheral nerve gangliosides (GM1, GD1a).
• Anti-GM1 or anti-GD1a IgG antibodies generated against the bacteria bind the axolemma at nodes of Ranvier, activate complement, and form the membrane-attack complex (MAC), causing conduction failure.
• Bradley and Daroff's Neurology in Clinical Practice, p. 2664

• Although the precise myelin antigen remains unidentified, autoantibodies (likely IgG, complement-fixing) bind to the inner layer of myelin - the earliest pathological event is complement deposition on myelin.
• Macrophages are the ultimate effectors: they strip away and destroy myelin sheaths (segmental demyelination) while initially sparing the axon.
• Both T-cell-mediated and antibody-mediated mechanisms operate; T cells sensitized to myelin antigens migrate through endoneurial vessel walls into the nerve parenchyma, with macrophages serving as the final destructive element. - Adams and Victor's Principles of Neurology, p. 1303

Step 3: Pathological Cascade in AIDP

Step 4: Why Areflexia is the Cardinal Sign

Step 5: Typical Clinical Progression Timeline

WEEK -3 to -1:  Antecedent infection (GI illness, respiratory infection, vaccination)
                ↓
DAY 1-7:        Distal sensory symptoms - paresthesias, tingling in toes and fingers
                Aching back/hip pain (may mimic viral myalgia or disc disease)
                ↓
DAY 3-14:       Progressive symmetric ascending weakness begins
                Legs → proximal legs → arms → facial muscles
                Areflexia - ankle jerks first, then all deep tendon reflexes
                ↓
WEEK 2-4:       PLATEAU - maximum deficit reached by 4 weeks (by definition)
                25-30% require mechanical ventilation (respiratory failure from diaphragm involvement)
                Autonomic dysfunction: labile BP, tachycardia/bradycardia, ileus, urinary retention
                Facial diplegia in >50%
                ↓
WEEK 4-8:       Plateau phase
                ↓
WEEKS to MONTHS: Recovery phase - remyelination and axonal regeneration
                80% achieve independent ambulation by 6 months

Electrophysiological Signature of AIDP

CSF Findings - Albuminocytological Dissociation

• Elevated protein (typically >45 mg/dL; often >100 mg/dL)
• Normal or near-normal cell count (<10 leukocytes/μL)

GBS Subtypes Comparison

Respiratory Monitoring - The Critical Emergency Issue

• FVC < 20 mL/kg (~1.5L in an average adult)
• Negative Inspiratory Force (NIF) worse than -30 cmH₂O
• An indirect bedside test: ask the patient to count in a single breath - each number ≈ 100 mL of VC

Treatment

Prognosis

• Disease progression reaches maximum (nadir) by 4 weeks (definitional)
• Recovery begins 2-4 weeks after plateau
• ~80% achieve good functional recovery (walk independently by 6 months)
• ~20% retain significant residual disability at 1 year
• Mortality 1-5% (was 33% before modern ventilatory support)
• Poorer prognosis: older age, rapid onset to nadir, preceding C. jejuni infection, axonal subtypes (AMAN/AMSAN), requirement for ventilation

GBS / AIDP - Based Exclusively on Harrison's Principles of Internal Medicine, 22nd Edition (2025)

PART 1: Differential Diagnosis for Acute Ascending Symmetrical Weakness + Distal Sensory Symptoms

1. Guillain-Barré Syndrome (Primary Consideration)

2. Spinal Cord Disease

3. Botulism

4. Tick Paralysis

5. Hypophosphataemia-Related Neuropathy

6. Lymphoma and Systemic Disease-Associated Neuropathies

7. Immune Checkpoint Inhibitor-Associated Neuropathy

PART 2: Pathophysiology, Immune Mechanisms, and Clinical Progression of GBS / AIDP

Definition

Antecedent Events and Triggers

Immunopathogenesis: The Central Concept - Molecular Mimicry

"Circumstantial evidence suggests that all GBS results from immune responses to nonself antigens (infectious agents, vaccines) that misdirect to host nerve tissue through a resemblance-of-epitope (molecular mimicry) mechanism." - Harrison's, p. 3661

• Gangliosides are exposed on the plasma membrane of cells, making them accessible to antibody attack.
• They are present in large quantities in nervous tissue, especially at nodes of Ranvier.
• Antiganglioside antibodies are found in 20-50% of GBS cases overall, and are particularly common in AMAN and AMSAN following C. jejuni infection.

• C. jejuni isolates from GBS patients have surface glycolipid structures that antigenically cross-react with gangliosides including GM1 concentrated in human nerves.
• Sialic acid residues from pathogenic C. jejuni strains also activate dendritic cells via TLR4 signaling, promoting B-cell differentiation and amplifying humoral autoimmunity.
• Anti-GM1 antibodies bind gangliosides at nodes of Ranvier → MAC formation → disappearance of voltage-gated sodium (Nav) channel clusters → paranodal myelin detachment → nerve conduction failure and muscle weakness.

Immunopathogenesis of AIDP (The Demyelinating Form)

• Autoantibodies bind myelin antigens on the outer surface of Schwann cells.
• This activates complement, leading to MAC (membrane-attack complex) formation on the Schwann cell surface.
• MAC initiates vesicular degeneration of myelin.
• Macrophages are subsequently recruited and invade the myelin sheath, acting as scavengers to remove myelin debris.
• Result: segmental demyelination - axons initially preserved.
• Harrison's, p. 3662 (Figure 458-2 description)

• IgG anti-GM1 or anti-GD1a autoantibodies bind the nodal and internodal axolemma of motor fibers.
• MAC forms at the node of Ranvier.
• Nav channel clusters disappear; paranodal myelin detaches.
• Nerve conduction failure occurs (axonal conduction block).
• Macrophages invade from the nodes into the periaxonal space, scavenging injured axons.
• Axonal degeneration follows at a later stage.
• Harrison's, p. 3663 (Figure 458-2 description)

GBS Subtypes and Their Antibodies (Harrison's Table 458-1 and Figure 458-1)

Clinical Progression - Harrison's Account

• Ascending paralysis first noticed as "rubbery legs"
• Tingling dysesthesias in extremities - begins distally in feet (matches the 1-week tingling history in our patient)
• Pain in the neck, shoulder, back, or diffusely over the spine in ~50% of patients - this may mimic viral myalgia or disc disease early on
• Deep tendon reflexes attenuate or disappear within the first few days of onset
• Fever and constitutional symptoms are absent at onset - "if present, cast doubt on the diagnosis"

• Progressive symmetric ascending weakness; legs more affected than arms
• Facial paresis in 50% of patients
• Lower cranial nerve involvement → bulbar weakness, difficulty handling secretions; "diagnosis may initially be mistaken for brainstem ischemia"
• Cutaneous sensory deficits (pain, temperature) are "usually relatively mild"
• Large-fibre sensory functions (proprioception, vibration, deep tendon reflexes) are more severely affected
• Bladder dysfunction may occur in severe cases but is "usually transient" - if prominent or early, consider spinal cord disease instead

• Occur even in "patients whose GBS is otherwise mild"
• Loss of vasomotor control, wide fluctuations in blood pressure, postural hypotension, cardiac dysrhythmias
• Harrison's specifically notes: "These features require close monitoring and management and can be fatal"

• Up to 30% require ventilatory assistance at some time during the illness
• Associated with: more severe weakness on admission, rapid tempo of progression, presence of facial/bulbar weakness in the first week

• "Once clinical worsening stops and the patient reaches a plateau (almost always within 4 weeks of onset), further progression is unlikely."

Diagnosis - Harrison's Three-Level Case Definition

• Bilateral flaccid limb weakness
• Decreased/absent deep tendon reflexes in weak limbs
• Monophasic illness; nadir reached between 12 hours and 28 days, then plateau
• Electrophysiologic findings consistent with GBS
• Cytoalbuminologic dissociation: CSF protein elevated above normal AND CSF WBC <50 cells/μL
• No alternative diagnosis identified

• Same clinical criteria
• CSF WBC <50 cells/μL (protein may be normal)
• OR if CSF unavailable: electrophysiology consistent with GBS

• Clinical criteria met
• No CSF or electrophysiology available to support
• No alternative diagnosis

Laboratory Investigations per Harrison's

• Cytoalbuminologic dissociation: elevated protein, <10 cells/μL (Harrison's cites <50 cells/μL as the threshold for Level 1 diagnosis)
• Normal CSF in first week does NOT exclude GBS - repeat LP after 1 week if clinically suspected
• If CSF pleocytosis is present: consider HIV, CMV polyradiculopathy, Lyme, sarcoidosis

• AIDP: demyelinating pattern - prolonged latencies, slowed conduction velocities, conduction block, absent/prolonged F-waves and H-reflexes
• AMAN: reduced CMAP amplitudes, normal SNAPs, no demyelinating features
• Harrison's notes: "If the diagnosis is strongly suspected, treatment should be initiated without waiting for evolution of the characteristic EDx and CSF findings"

• Anti-GM1 antibodies: positive in 20-50% of GBS overall; more common in AMAN
• Anti-GQ1b antibodies: >90% in Miller Fisher syndrome
• HIV serology: if risk factors present or if CSF pleocytosis found

Treatment per Harrison's

"In the vast majority of patients with GBS, treatment should be initiated as soon after diagnosis as possible. Each day counts; ~2 weeks after the first motor symptoms, it is not known whether immunotherapy is still effective."