| Characteristics | Acute myelitis | Guillain-Barré syndrome | Distinguishing features |
| Motor findings | Paraparesis or quadriparesis | Ascending weakness LE>UE in the early stages | Myelopathy: if UE involvement, often as severe as LE; often no UE involvement GBS: there usually is UE involvement and it is less severe than LE involvement early in the disease |
| Sensory findings | Usually can diagnosis a spinal cord level | Ascending sensory loss LE>UE in the early stages | Myelopathy: sensory level usually identified; often no arm involvement GBS: no sensory level; usually UE less affected than LE early in the disease |
| Autonomic findings | Early loss of bowel and bladder control | Autonomic dysfunction of the cardiovascular system | Myelopathy: urinary urgency or retention early and prominent; cardiovascular instability only in severe cases higher than T6 spinal level GBS: urinary urgency or retention less common; cardiovascular instability is more common |
| Cranial nerve findings | None | Extra-ocular muscle palsies or facial weakness | GBS: cranial neuropathies are more common than in acute myelopathy |
| Electrophysiologic findings | EMG/NCV findings may be normal or may implicate the spinal cord Prolonged central conduction on somatosensory evoked potential (SEP) latencies or missing SEP in conjunction with normal sensory nerve action potentials | EMG/NCV findings confined to the peripheral nervous system: motor and/or sensory nerve conduction velocity reduced, distal latencies prolonged; conduction block; reduced H reflex usually present | The lack of peripheral nerve abnormalities in a patient with progressive weakness and sensory loss should suggest evaluation of the spinal cord for pathology Conversely, patients with suspected acute myelopathy but equivocal clinical, laboratory, or radiologic findings may warrant peripheral nerve examination |
| MRI findings | Usually a focal area of increased T2 signal in the spinal cord, with or without gadolinium enhancement | May be normal, or may reveal thickening and enhancement of the intrathecal spinal nerve roots and cauda equina. Abnormalities of the posterior columns are described in exceptional cases of Miller Fisher syndrome | MRI abnormalities may be helpful in diagnosing a patient who is suspected of having GBS from acute myelopathy |
| CSF | Usually, CSF pleocytosis and/or increased IgG index | Usually, elevated protein in the absence of CSF pleocytosis | CSF pleocytosis and elevated IgG index may be helpful in diagnosing a patient who is suspected of having GBS from acute myelopathy |
