Guillain-Barré Syndrome: Electromyography is the Most Likely Diagnostic Test
Electromyography of the lower extremity is the most appropriate diagnostic test for this patient presenting with ascending bilateral weakness, paresthesias, and areflexia, which is classic for Guillain-Barré syndrome (GBS).
Clinical Presentation Analysis
This patient demonstrates the hallmark features of GBS:
- Ascending symmetric weakness that began in the lower extremities approximately one week ago and progressed acutely, preventing her from stepping out of a jacuzzi (indicating rapid functional decline)
- Bilateral paresthesias affecting both lower extremities in an asymmetric distribution (right below knee, left quadriceps)
- Hyporeflexia/areflexia with diminished patellar reflex (1+ on left, 2+ on right) - a critical finding that distinguishes GBS from other causes of weakness
- Associated cranial nerve involvement suggested by occasional diplopia and fatigue
- Temporal progression over approximately one week, consistent with the typical GBS timeline
Why Electromyography is Diagnostic
Electromyography with nerve conduction studies is the gold standard for confirming GBS diagnosis. The test will demonstrate:
- Demyelinating features including prolonged distal latencies, conduction velocity slowing, temporal dispersion, and conduction block in the acute inflammatory demyelinating polyneuropathy (AIDP) variant
- Reduced compound muscle action potential amplitudes indicating axonal involvement
- Absent or prolonged F-waves, which are often the earliest electrodiagnostic abnormality in GBS
- Prolonged or absent H-reflexes, particularly sensitive in early disease
These findings directly confirm the peripheral nerve pathology characteristic of GBS and distinguish it from central nervous system disorders.
Why Other Tests Are Not Appropriate
Computed tomography angiography of the brain would be indicated for stroke evaluation, but this patient's bilateral symmetric ascending weakness with areflexia is inconsistent with a vascular CNS event. Stroke typically presents with acute unilateral weakness, hyperreflexia (upper motor neuron signs), and does not cause the progressive ascending pattern seen here.
Gram stain and culture of cerebrospinal fluid would be appropriate for bacterial meningitis, but this patient lacks fever, meningismus, altered mental status, or other signs of acute CNS infection. While CSF analysis showing albuminocytologic dissociation (elevated protein with normal cell count) supports GBS diagnosis, it is not diagnostic and may be normal in the first week of illness. CSF studies are supportive but not the primary diagnostic test.
Magnetic resonance imaging of the spine with contrast would be indicated for spinal cord compression, transverse myelitis, or structural lesions 1, 2, 3, 4, 5. However, this patient's areflexia definitively excludes upper motor neuron pathology - spinal cord lesions cause hyperreflexia, not hyporeflexia. MRI would show enhancement of nerve roots in GBS but is not necessary for diagnosis and is less specific than EMG.
Critical Clinical Pitfalls
The most dangerous error would be delaying diagnosis while pursuing unnecessary imaging. GBS can progress rapidly to respiratory failure requiring mechanical ventilation, and early recognition is essential for:
- Monitoring respiratory function with serial vital capacity measurements and negative inspiratory force
- Initiating immunotherapy with intravenous immunoglobulin (IVIG) or plasmapheresis, which improves outcomes when started early
- Preventing complications including autonomic instability, deep vein thrombosis, and aspiration
Do not be misled by the jacuzzi exposure - while the warm water may have transiently worsened symptoms (heat sensitivity can occur with demyelinating disorders), the progressive ascending weakness over one week is the key feature, not the acute worsening in the jacuzzi.
The absence of recent infection history does not exclude GBS - while two-thirds of cases follow respiratory or gastrointestinal infection, many patients do not recall a preceding illness. The absence of tick exposure appropriately excludes Lyme disease, which can cause peripheral neuropathy but typically presents differently 6.