Diagnostic Evaluation: Acute Flaccid Paralysis with Atypical Features
Critical Diagnostic Concern
This presentation has several features that cast significant doubt on a diagnosis of Guillain-Barré syndrome and should prompt urgent investigation for alternative diagnoses, particularly acute transverse myelitis or spinal cord compression. 1
The combination of bilateral extensor plantar responses (Babinski sign) and increased lower-limb tone are red flags that strongly suggest upper motor neuron pathology rather than the peripheral nerve disease typical of GBS. 1
Why This Is NOT Classic Guillain-Barré Syndrome
Features That Cast Doubt on GBS Diagnosis
Extensor plantar responses (bilateral Babinski signs) are explicitly listed as features that cast doubt on GBS diagnosis in the National Institute of Neurological Disorders and Stroke criteria, as they indicate corticospinal tract involvement rather than peripheral nerve pathology. 1
Increased tone (spasticity) in the lower limbs contradicts the expected hypotonia or flaccidity of GBS, where muscle tone is typically reduced or normal due to lower motor neuron involvement. 1
The combination of absent reflexes with extensor plantars and increased tone is internally inconsistent and suggests a mixed upper and lower motor neuron process, or acute spinal shock transitioning to spasticity. 1
What These Signs Actually Indicate
Bilateral extensor plantar responses indicate bilateral corticospinal tract dysfunction, which localizes the pathology to the spinal cord, brainstem, or bilateral cerebral hemispheres—not the peripheral nerves. 1
Increased lower-limb tone suggests upper motor neuron involvement, though in very acute spinal cord lesions there may be an initial period of "spinal shock" with flaccidity and areflexia that transitions to spasticity within hours to days. 1
Most Likely Alternative Diagnoses
Acute Transverse Myelitis
Acute transverse myelitis can present with rapidly progressive bilateral lower-limb weakness, sensory level (which may be subtle or absent initially), and bladder/bowel dysfunction that may not be apparent in the first 24-48 hours. 1
In the hyperacute phase, reflexes may be absent due to spinal shock, but extensor plantar responses and increased tone indicate evolving upper motor neuron pathology. 1
Post-infectious transverse myelitis can follow upper respiratory infections, making the temporal relationship with URTI 10 days prior highly relevant. 1
Spinal Cord Compression
Epidural abscess, hematoma, or tumor can cause acute bilateral lower-limb weakness with upper motor neuron signs. 1
The absence of back pain does not exclude spinal pathology, as some compressive lesions present without significant pain. 1
Immediate Diagnostic Workup
Urgent Neuroimaging (Do NOT Delay)
Obtain MRI of the entire spine with and without gadolinium contrast immediately to rule out compressive lesions (epidural abscess, hematoma, tumor) and to evaluate for intramedullary signal abnormality consistent with transverse myelitis. 1, 2
MRI should be performed before lumbar puncture if there is any concern for spinal cord pathology, as LP can worsen herniation in cases of mass effect. 1
Neurology Consultation
- Obtain immediate neurology consultation for every patient with suspected acute myelopathy or atypical GBS presentation. 1, 2, 3
Cerebrospinal Fluid Analysis (After Imaging)
Perform lumbar puncture after MRI to assess for albuminocytologic dissociation (elevated protein with normal cell count, typical of GBS) versus pleocytosis (elevated white cells, suggesting inflammatory or infectious myelitis). 1, 2, 4
Marked CSF pleocytosis (>50 cells/μL) strongly suggests alternative diagnoses such as infectious or inflammatory myelitis, though mild pleocytosis (10-50 cells/μL) can occur in GBS. 1
Send CSF for cell count with differential, protein, glucose, cytology, bacterial and viral cultures, oligoclonal bands, and IgG index to evaluate for inflammatory or infectious causes. 1, 2
Electrodiagnostic Studies
Nerve conduction studies and EMG should be performed to look for evidence of peripheral nerve involvement (reduced conduction velocities, reduced amplitudes, temporal dispersion, conduction blocks). 1, 2, 4
However, electrophysiological measurements may be normal when performed within the first week of symptom onset, so normal early studies do not exclude GBS. 1
The "sural sparing pattern" (normal sural sensory nerve action potential with abnormal median/ulnar responses) is typical for GBS and can help differentiate it from other neuropathies. 1, 2
Additional Laboratory Tests
Complete blood count, glucose, electrolytes, renal function, liver enzymes, and creatine kinase to exclude metabolic causes of weakness and to assess for rhabdomyolysis. 2
Serum antiganglioside antibody testing (including anti-GQ1b for Miller-Fisher variant) can support the diagnosis of GBS but should not delay treatment. 1, 2
Management Approach
If Spinal Cord Pathology Is Confirmed
Acute transverse myelitis requires high-dose intravenous methylprednisolone (1 g/day for 3-5 days) as first-line therapy, not IVIg or plasma exchange. 1
Compressive lesions require urgent neurosurgical consultation for possible decompression. 1
If GBS Is Confirmed (After Excluding Myelopathy)
Initiate IVIg 0.4 g/kg/day for 5 consecutive days (total 2 g/kg) for any patient unable to walk unaided within 2-4 weeks of symptom onset. 2, 3, 4
Plasma exchange (200-250 mL/kg over 4-5 sessions) is an equally effective alternative to IVIg. 2, 3, 4
Do NOT use corticosteroids alone for idiopathic GBS, as they have not been shown to improve outcomes. 2, 3, 4
Respiratory and Autonomic Monitoring
Assess respiratory function immediately with vital capacity, negative inspiratory force (NIF), and maximum inspiratory/expiratory pressures, as approximately 20% of GBS patients develop respiratory failure. 2, 3
Apply the "20/30/40 rule": patient is at risk of respiratory failure if vital capacity <20 mL/kg, maximum inspiratory pressure <30 cmH₂O, or maximum expiratory pressure <40 cmH₂O. 2, 3
Continuously monitor heart rate, blood pressure, and ECG for autonomic dysfunction (arrhythmias, blood pressure instability), which contributes to the 3-10% mortality rate in GBS. 2, 3
Admit to an inpatient unit with capability for rapid ICU transfer for any patient with severe weakness, dysphagia, facial weakness, respiratory muscle weakness, or rapidly progressive symptoms. 1, 2, 3
Common Pitfalls to Avoid
Do Not Assume GBS Based on Post-Infectious Timing Alone
- The history of URTI 10 days prior is consistent with both GBS and post-infectious transverse myelitis, so the temporal relationship alone does not distinguish between these diagnoses. 1, 5
Do Not Dismiss Myelopathy Based on Absent Sensory Level
- Acute transverse myelitis can present without an obvious sensory level in the early stages, and the absence of sensory symptoms does not exclude spinal cord pathology. 1
Do Not Ignore Upper Motor Neuron Signs
- Extensor plantar responses and increased tone are NOT compatible with uncomplicated GBS and mandate urgent spinal imaging. 1
Do Not Delay Imaging to Perform LP First
- MRI of the spine must be obtained before lumbar puncture if there is any suspicion of spinal cord pathology, as LP can worsen herniation in cases of mass effect. 1
Prognosis Depends on Correct Diagnosis
If GBS Is Confirmed
Approximately 80% of GBS patients regain independent walking ability at 6 months, with recovery continuing for up to 3 years or longer. 2, 3, 4
Mortality is 3-10%, primarily from cardiovascular and respiratory complications. 2, 3, 4