Which clinical feature best distinguishes Guillain-Barré Syndrome (GBS) from acute transverse myelitis (ATM)?

Explanation

## Distinguishing GBS from Acute Transverse Myelitis ### Key Discriminating Feature **Key Point:** Ascending paralysis with areflexia is the hallmark of GBS and distinguishes it from ATM, which typically presents with a sensory level and preserved or hyperactive reflexes below the lesion. ### Comparative Clinical Features | Feature | GBS | Acute Transverse Myelitis | |---------|-----|---------------------------| | **Reflex pattern** | Areflexia (lost early) | Hyperreflexia or normal below level | | **Progression** | Ascending (legs → trunk → arms) | Non-ascending; sensory level | | **Sensory findings** | Distal, symmetric; no level | Clear sensory level (hallmark) | | **Bowel/bladder** | Late or absent | Early involvement (spinal cord sign) | | **CSF protein** | Elevated (albuminocytologic dissociation) | Mildly elevated or normal | | **MRI spine** | Normal | T2 hyperintensity in cord | ### Pathophysiology **Clinical Pearl:** GBS is a demyelinating polyradiculoneuropathy affecting peripheral nerves and nerve roots, causing loss of reflexes due to disruption of the reflex arc. ATM is a myelitis (spinal cord inflammation), which typically preserves or enhances reflexes due to upper motor neuron involvement below the lesion. ### High-Yield Mnemonic **Mnemonic: GABS** — GBS = Ascending, Bilateral, areflexia, Symmetric **Mnemonic: ATM-LEVEL** — ATM = sensory Level, Early bladder, Vertical cord lesion, Enhanced reflexes, Lesion on MRI ### Clinical Reasoning In GBS, the autoimmune attack targets the peripheral nervous system (myelin or axons), causing demyelination of motor nerves and nerve roots. This interrupts the reflex arc at the peripheral level, resulting in areflexia. The ascending pattern reflects the proximal-to-distal progression of demyelination. In contrast, ATM damages the spinal cord itself, preserving or exaggerating reflexes below the lesion due to loss of descending inhibitory input (upper motor neuron signs).