Physiology · Year 1 · from Physiology
Case 2: Guillain-Barre Syndrome - Peripheral Demyelination
Clinical Image
Source: Wikimedia Commons - Guillain-Barre Syndrome - CC BY-SA 4.0
Patient Presentation
A 45-year-old male presents to the emergency department with progressive weakness in both legs that began 3 days ago and has now spread to involve his arms. He reports tingling and numbness in his hands and feet. Two weeks ago, he had a gastrointestinal illness with diarrhea that resolved after several days. He now has difficulty walking and climbing stairs.
Demographics
- Age: 45 years
- Sex: Male
- Recent history: Gastroenteritis 2 weeks prior (likely Campylobacter jejuni infection)
Chief Complaint
Progressive ascending weakness and paresthesias
Physical Examination
- Vital signs: BP 142/88, HR 98, RR 18, SpO2 96% on room air
- General: Anxious, mildly dyspneic when supine
- Motor: 3/5 strength in proximal lower extremities, 4/5 in distal lower extremities, 4/5 throughout upper extremities
- Reflexes: Absent in ankles and knees, diminished in upper extremities (areflexia)
- Sensory: Decreased light touch and vibration in stocking-glove distribution
- Gait: Unable to walk without assistance
- Respiratory: Negative inspiratory force (NIF) -35 cmH2O (borderline; normal > -60)
- Cranial nerves: Intact at this time
Workup
- Lumbar puncture: Protein 125 mg/dL (elevated), WBC 3 cells/uL (albuminocytologic dissociation - elevated protein without pleocytosis)
- Nerve conduction studies (NCS): Prolonged distal motor latencies, reduced conduction velocities (32 m/s; normal >50 m/s), temporal dispersion, conduction block - consistent with demyelinating polyneuropathy
- EMG: No active denervation (early stage)
- Anti-ganglioside antibodies: Positive for anti-GM1 antibodies
- Stool culture: Campylobacter jejuni (retrospective confirmation)
- Serial pulmonary function: NIF and FVC monitored q4-6 hours
Diagnosis
Guillain-Barre Syndrome (Acute Inflammatory Demyelinating Polyneuropathy - AIDP) with impending respiratory compromise
Treatment
- ICU admission for respiratory monitoring
- Serial measurement of NIF and FVC (intubate if NIF < -25 or FVC < 20 mL/kg)
- Intravenous immunoglobulin (IVIG) 0.4 g/kg/day for 5 days OR plasmapheresis (5 exchanges over 2 weeks)
- DVT prophylaxis (high risk for immobility-related thrombosis)
- Pain management for neuropathic pain
- Physical and occupational therapy
- Monitor for autonomic dysfunction (blood pressure lability, arrhythmias)
- Nutritional support
- Psychological support and counseling regarding recovery timeline (weeks to months)
Physiological Principles Demonstrated
- Compound action potential: The nerve conduction study measures the summated electrical activity of all axons in a peripheral nerve. In GBS, demyelination causes prolonged distal latencies and slowed conduction velocities.
- Temporal dispersion: Different axons conduct at different velocities when variably demyelinated, causing the compound action potential to spread out over time and decrease in amplitude.
- Conduction block: When demyelination is severe enough, the local current generated by an action potential cannot reach threshold at the next segment, causing complete conduction failure. This manifests as a >50% amplitude drop between proximal and distal stimulation sites.
- Fiber classification: Motor fibers (A-alpha, largest and fastest) and large sensory fibers are affected early. The ascending pattern reflects the greater vulnerability of longer axons.
- Schwann cell attack: Autoimmune attack on Schwann cell myelin (triggered by molecular mimicry with Campylobacter lipooligosaccharides resembling gangliosides) disrupts the myelin sheath, exposing the axon membrane.
- Areflexia mechanism: Deep tendon reflexes depend on intact afferent (Ia sensory) and efferent (alpha motor neuron) conduction. Demyelination of either component abolishes the reflex.