What investigations should be done for a patient suspected of having Guillain-Barré Syndrome (GBS)?

Diagnostic Investigations for Guillain-Barré Syndrome

A comprehensive diagnostic workup for suspected Guillain-Barré Syndrome (GBS) should include neurological consultation, cerebrospinal fluid analysis, electrodiagnostic studies, and selected laboratory tests to confirm the diagnosis and rule out mimics.

Initial Clinical Assessment

• Evaluate for progressive, typically symmetrical muscle weakness with absent or reduced deep tendon reflexes, often starting with sensory symptoms in the lower back and thighs 1
• Document any recent history of diarrhea or respiratory infection, which strongly supports GBS diagnosis 2
• Assess for involvement of facial, respiratory, bulbar, and oculomotor nerves 1
• Monitor for signs of autonomic dysfunction (blood pressure fluctuations, arrhythmias) 1

Essential Diagnostic Tests

Cerebrospinal Fluid (CSF) Examination

• Perform lumbar puncture during initial evaluation to look for albumino-cytological dissociation (elevated protein with normal cell count) 1
• Note that protein levels may be normal in 30-50% of patients in the first week and 10-30% in the second week 1
• Marked pleocytosis (>50 cells/μl) suggests alternative diagnoses 1
• Include cytology for malignant cells in patients with cancer 1

Electrodiagnostic Studies

• Conduct nerve conduction studies (NCS) and electromyography (EMG) to support diagnosis and differentiate GBS subtypes 1
• Look for characteristic findings: reduced conduction velocities, reduced sensory and motor evoked amplitudes, abnormal temporal dispersion, and/or partial motor conduction blocks 1
• The H-reflex is the most sensitive test for early GBS (absent in 97% of patients within first week) 3
• Consider repeat studies 2-3 weeks later if initial results are normal or inconclusive 1

Laboratory Investigations

• Complete blood counts, glucose, electrolytes, kidney function, and liver enzymes to exclude other causes of acute flaccid paralysis 1
• Consider testing for anti-ganglioside antibodies, especially anti-GQ1b antibodies when Miller Fisher variant is suspected 1
• Screen for reversible neuropathy causes: HbA1c, vitamin B12, folate, TSH, HIV 1

Additional Investigations

Imaging Studies

• MRI of spine with and without contrast to rule out compressive lesions and evaluate for nerve root enhancement/thickening 1
• Consider MRI brain if cranial nerve involvement is present 1
• Ultrasound imaging of peripheral nerves may reveal enlarged cervical nerve roots early in disease course 1

Specialized Testing

• Consider paraneoplastic workup (e.g., ANNA-1 antibody testing) 1
• Test for nodal-paranodal antibodies when autoimmune nodopathy is suspected 2
• In Miller Fisher variant, test for anti-GQ1b antibodies (found in up to 90% of cases) 1

Monitoring for Respiratory Compromise

• Perform pulmonary function testing (negative inspiratory force/vital capacity) 1
• Monitor for signs of respiratory distress: breathlessness at rest or during talking, inability to count to 15 in a single breath, use of accessory respiratory muscles 1
• Implement frequent neurological checks to assess for progression 1

Important Considerations

• Diagnosis is primarily clinical but supported by ancillary investigations 1
• Normal CSF protein does not rule out GBS, especially in the first week 1
• Consider GBS variants (Miller Fisher syndrome, pharyngeal-cervical-brachial, paraparetic) which may present atypically 1
• Be vigilant for treatment-related fluctuations (10% of patients) and acute-onset CIDP (5% of patients initially diagnosed with GBS) 4, 2
• Pain can be a confusing early symptom that may precede weakness 4, 5

By following this diagnostic algorithm, clinicians can promptly diagnose GBS and initiate appropriate treatment, which is crucial as early intervention improves outcomes 4.