What is the diagnostic approach to Guillain-Barré Syndrome (GBS)?

Diagnostic Approach to Guillain-Barré Syndrome (GBS)

The diagnosis of Guillain-Barré Syndrome (GBS) requires a combination of clinical history, neurological examination, cerebrospinal fluid analysis, and electrodiagnostic studies, with clinical features being the cornerstone of diagnosis. 1

Clinical Features to Identify

Typical Presentation

• Rapidly progressive bilateral weakness of legs and/or arms, often ascending in pattern, reaching maximum disability within 2 weeks 1
• Decreased or absent tendon reflexes in affected limbs 1
• Distal paresthesias or sensory loss preceding or accompanying weakness 1
• Relative symmetry of symptoms and signs 1
• Pain (muscular, radicular, or neuropathic) is frequently reported 1
• Autonomic dysfunction (blood pressure/heart rate instability, pupillary dysfunction, bowel/bladder dysfunction) 1
• Cranial nerve involvement, especially bilateral facial palsy 1

Atypical Presentations and Variants

• Weakness may be asymmetrical or predominantly proximal/distal 1
• Weakness can start in legs, arms, or simultaneously in all limbs 1
• Severe pain or isolated cranial nerve dysfunction may precede weakness 1
• Miller Fisher syndrome: ophthalmoplegia, ataxia, and areflexia (5-25% of cases) 1
• Pure motor variant: weakness without sensory signs (5-70% of cases) 1
• Other variants: pharyngeal-cervical-brachial, paraparetic, bilateral facial palsy, pure sensory 1

Warning Signs (Features Casting Doubt on Diagnosis)

• Marked pleocytosis in CSF (>50 cells/μl) 1
• Persistent asymmetry of weakness 1
• Bladder/bowel dysfunction at onset 1
• Severe respiratory dysfunction with limited limb weakness at onset 1
• Fever at onset 1
• Nadir <24 hours or progression >4 weeks 1
• Sharp sensory level suggesting spinal cord injury 1
• Hyperreflexia or extensor plantar responses 1

Diagnostic Algorithm

Step 1: Clinical Assessment

• Document pattern and progression of weakness 1
• Assess tendon reflexes 1
• Evaluate for sensory symptoms 1
• Check for cranial nerve involvement 1
• Look for signs of autonomic dysfunction 1
• Inquire about preceding events (infections within 6 weeks) 1

Step 2: Laboratory Investigations

• Complete blood count, glucose, electrolytes, kidney function, liver enzymes (to exclude other causes) 1
• Anti-ganglioside antibody testing:
  • Limited value in typical GBS but may help when diagnosis is uncertain 1
  • Anti-GQ1b antibodies have greater diagnostic value in suspected Miller Fisher syndrome (present in up to 90% of cases) 1

Step 3: Cerebrospinal Fluid Examination

• Look for albumino-cytological dissociation (elevated protein with normal cell count) 1
• Important note: Normal protein levels do not rule out GBS (30-50% normal in first week, 10-30% normal in second week) 1
• Mild pleocytosis (10-50 cells/μl) is compatible but should prompt consideration of alternative diagnoses 1

Step 4: Electrodiagnostic Studies

• Not required for diagnosis but recommended to support it, particularly in atypical presentations 1
• Typical findings: reduced conduction velocities, reduced sensory and motor evoked amplitudes, abnormal temporal dispersion, partial motor conduction blocks 1
• "Sural sparing pattern": normal sural sensory nerve action potential with abnormal median and ulnar sensory nerve action potentials 1
• Note: Studies may be normal early in disease course (within 1 week of onset) or in certain variants 1
• Consider repeat studies 2-3 weeks later if initial results are normal but clinical suspicion remains high 1

Step 5: Imaging (in Selected Cases)

• MRI or ultrasound imaging should be considered in atypical cases 2

Important Diagnostic Considerations

Timing of Symptom Progression

• Classic GBS: progressive phase lasts from days to 4 weeks (usually <2 weeks) 1
• If maximum disability is reached within 24 hours or after 4 weeks, consider alternative diagnoses 1
• Consider changing diagnosis to acute-onset chronic inflammatory demyelinating polyradiculoneuropathy (A-CIDP) if progression continues after 8 weeks from onset (occurs in approximately 5% of patients initially diagnosed with GBS) 2, 3

Diagnostic Pitfalls to Avoid

• Relying solely on CSF protein levels (may be normal early in disease) 1
• Waiting for antibody test results before initiating treatment 1
• Dismissing diagnosis due to normal initial electrodiagnostic studies 1
• Failing to recognize atypical presentations, especially in young children who may present with nonspecific features (pain, refusal to bear weight, irritability) 1
• Missing treatment-related fluctuations (TRFs), which occur in a minority of patients and may be confused with disease progression 3

By following this structured diagnostic approach, clinicians can accurately diagnose GBS and its variants, allowing for prompt treatment initiation which is crucial for improving outcomes 2, 4.