How to differentiate between ascending transverse myelitis vs AMSAN variant of GBS
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"transverse myelitis" AND "Guillain-Barre syndrome"
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transverse myelitis versus Guillain Barre syndrome differentiating MRI CSF nerve conduction guideline
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https://pmc.ncbi.nlm.nih.gov/articles/PMC11235944/
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The key distinction is spinal cord disease (transverse myelitis) versus peripheral motor and sensory axon disease (AMSAN, an axonal Guillain-Barré syndrome subtype). “Ascending weakness” alone does not distinguish them.
| Feature | Ascending transverse myelitis | AMSAN variant of GBS |
|---|---|---|
| Site of lesion | Spinal cord | Peripheral nerves and roots |
| Weakness | Often bilateral leg weakness that may ascend, with a definable cord level | Symmetric, rapidly progressive flaccid weakness, usually legs first, often severe |
| Sensory symptoms | Clear sensory level on trunk is the most useful clinical clue | Distal, length-dependent sensory loss or paresthesia. No sensory level |
| Tone and plantar response | Initially may be flaccid with absent reflexes from spinal shock, but later develops spasticity, hyperreflexia, and extensor plantar responses below lesion | Flaccid tone, hyporeflexia/areflexia persist. Plantars flexor or absent, not extensor |
| Bladder/bowel dysfunction | Usually early and prominent: retention, incontinence, constipation, sexual dysfunction | May occur in severe disease but is generally transient and not an early dominant feature |
| Pain | Radicular or central back pain may occur | Neuropathic limb/back pain common, but not localizing |
| Cranial nerves / bulbar / respiratory weakness | Unusual unless very high cervical cord involvement | Commoner: facial weakness, bulbar weakness, and respiratory muscle involvement suggest GBS |
| Autonomic signs | Bladder/bowel dysfunction tied to cord lesion | BP lability, tachy/bradyarrhythmia, ileus, sweating abnormalities are typical dysautonomia |
| MRI spine with gadolinium | Intramedullary T2 hyperintense cord lesion, often enhancing. Longitudinally extensive lesion is possible | Cord parenchyma normal. Root enhancement can occur but is nonspecific |
| CSF | Inflammatory pattern is common: pleocytosis and/or raised IgG index, depending on cause | Albuminocytologic dissociation: elevated protein with usually <10 WBC/µL, though this may be absent in the first week |
| NCS/EMG | Peripheral nerve conduction typically normal | Axonal motor and sensory neuropathy: markedly reduced/absent CMAPs and SNAPs, relatively preserved conduction velocity and distal latency, without demyelinating features. May be falsely nondiagnostic very early, so repeat testing is needed |
| Course | May progress over hours to days, often reaches nadir by about 3 weeks | Progresses over hours to days, reaches nadir within 4 weeks |
Practical bedside rule
Think transverse myelitis if there is:
- A sensory level
- Early urinary retention or bowel dysfunction
- Upper motor neuron signs, although these can be masked initially by spinal shock
- A cord lesion on MRI or inflammatory CSF
Think AMSAN if there is:
- Symmetric flaccid areflexic quadriparesis
- Distal sensory involvement but no truncal sensory level
- Cranial, bulbar, or respiratory muscle involvement
- Axonal motor and sensory abnormalities on nerve-conduction studies
- Raised CSF protein with few cells
A normal spinal MRI strongly weighs against myelitis, but it does not fully exclude very early or technically inadequate imaging. Conversely, absent reflexes do not rule out acute myelitis because early cord lesions can cause spinal shock.
Important diagnostic workflow in an acute presentation
- Urgent MRI of the entire spine with contrast first, mainly to exclude compressive myelopathy, cord infarction, and inflammatory cord lesions.
- Lumbar puncture: cell count, protein, glucose, oligoclonal bands/IgG index, and targeted infectious studies.
- NCS/EMG, including sensory studies, with repeat testing after 1 to 2 weeks if the initial study is early or equivocal.
- Monitor forced vital capacity, negative inspiratory force, ECG, and autonomic instability if GBS/AMSAN is plausible.
- If myelitis is supported, investigate cause: AQP4-IgG, MOG-IgG, autoimmune and infectious testing as clinically indicated.
A fulminant transverse myelitis can cause loss of motor and sensory function below a cord level with bladder, bowel, and sexual dysfunction, while AMSAN is characterized by severe involvement of both motor and sensory axons. Goldman-Cecil Medicine, p. 3995; Harrison’s Principles of Internal Medicine, GBS section. A recent GBS diagnostic review similarly emphasizes that a sensory level and spinal MRI are the central discriminators when acute myelopathy mimics GBS.
Clinical caution: acute progressive weakness with urinary retention, a sensory level, breathing difficulty, dysphagia, or autonomic instability needs urgent hospital neurologic assessment. Transverse myelitis and AMSAN have different first-line treatment approaches, and occasionally can coexist in post-infectious immune syndromes.
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