How do you diagnose Guillain-Barré Syndrome (GBS)?

Diagnosing Guillain-Barré Syndrome (GBS)

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

Clinical Presentation Assessment

Core Clinical Features

• Rapidly progressive bilateral weakness of legs and/or arms
• Progression to maximum disability within 2 weeks (suspicion should be raised if maximum disability occurs within 24 hours or after 4 weeks)
• Decreased or absent reflexes in most patients at presentation and almost all at nadir
• Distal paresthesias or sensory loss preceding or accompanying weakness
• Monophasic clinical course (though treatment-related fluctuations occur in a minority)

Common Associated Features

• Dysautonomia (blood pressure/heart rate instability, pupillary dysfunction, bowel/bladder dysfunction)
• Pain (muscular, radicular, or neuropathic)
• Cranial nerve involvement (particularly facial nerve)

Atypical Presentations to Consider

• Asymmetrical weakness (though always bilateral)
• Predominantly proximal or distal weakness
• Severe pain preceding weakness
• Normal or exaggerated reflexes (particularly in pure motor variant with AMAN subtype)
• In children <6 years: poorly localized pain, refusal to bear weight, irritability, meningism

GBS Variants

Variant	Clinical Features
Pure motor	Motor weakness without sensory signs
Paraparetic	Paresis restricted to the legs
Pharyngeal-cervical-brachial	Weakness of pharyngeal, cervical, brachial muscles without lower limb weakness
Bilateral facial palsy	Bilateral facial weakness with paresthesias and reduced reflexes
Miller Fisher syndrome (MFS)	Ophthalmoplegia, ataxia, areflexia
Bickerstaff brainstem encephalitis	Ophthalmoplegia, ataxia, areflexia, pyramidal signs, impaired consciousness

Laboratory Investigations

Cerebrospinal Fluid (CSF) Examination

• Key finding: Albumino-cytological dissociation (elevated protein with normal cell count)
• Important notes:
  • Protein levels are normal in 30-50% of patients in first week
  • Normal CSF protein does not rule out GBS
  • Marked pleocytosis (>50 cells/μl) suggests alternative diagnoses
  • Mild pleocytosis (10-50 cells/μl) should prompt consideration of infectious causes

Electrodiagnostic Studies

• While not required for diagnosis, these studies are highly recommended to:
  • Support the diagnosis
  • Distinguish between subtypes (AIDP, AMAN, AMSAN)
  • Rule out alternative diagnoses
• Conduction block is a major abnormality, with absent H-reflex noted in >90% of patients 2

Additional Laboratory Testing

• Complete blood counts
• Blood glucose, electrolytes, kidney function, liver enzymes
• Anti-ganglioside antibodies:
  • Limited diagnostic value in typical GBS
  • Anti-GQ1b antibodies have greater value in suspected MFS (found in up to 90% of cases)
  • Negative results do not rule out GBS
• Nodal-paranodal antibodies when autoimmune nodopathy is suspected 3

Imaging

• MRI or ultrasound imaging should be considered in atypical cases 3
• Not routinely required for typical presentations

Diagnostic Algorithm

1. Initial assessment: Evaluate for rapidly progressive bilateral weakness with reduced/absent reflexes
2. History: Document preceding events (infections in previous 6 weeks occur in ~2/3 of cases)
3. Examination: Assess pattern of weakness, sensory involvement, reflexes, cranial nerves
4. CSF examination: Look for albumino-cytological dissociation
5. Electrodiagnostic studies: Support diagnosis and determine subtype
6. Consider variants: Evaluate for specific clinical patterns of GBS variants
7. Rule out mimics: Consider alternative diagnoses, especially with atypical features

Common Pitfalls and Caveats

• Misdiagnosis in early presentation: Pain may precede weakness, leading to confusion with other conditions 4
• Normal CSF protein: Does not rule out GBS, especially in first week
• Atypical reflexes: Some variants may have preserved or even exaggerated reflexes
• Progression beyond 4 weeks: Consider acute-onset chronic inflammatory demyelinating polyradiculoneuropathy (A-CIDP), which occurs in about 5% of patients initially diagnosed with GBS 3, 4
• Treatment-related fluctuations: Secondary deterioration within 8 weeks after initial treatment occurs in about 10% of patients 4
• Overlooking respiratory compromise: Monitor respiratory function in all patients as respiratory failure can occur without symptoms of dyspnea 1

By systematically evaluating these clinical, laboratory, and electrophysiological features, clinicians can accurately diagnose GBS and its variants, allowing for prompt treatment and improved outcomes.