TABLE 4.

Diagnostic Findings and Clinical Course of Acute Flaccid Myelitis Compared to Other Neurological Syndromes With Acute Limb Weakness

		Acute Flaccid Myelitis Cases in the United States 2012–2015	Idiopathic Transverse Myelitis	Acute Inflammatory Demyelinating Polyneuropathy	Acute Disseminated Encephalomyelitis
Diagnostic findings	CSF features	Mild pleocytosis;normal to mildly elevated protein	Lymphocytic pleocytosis in half; elevated protein	No pleocytosis;elevated protein	Lymphocytic pleocytosis; elevated protein
	Imaging features	Confluent, longitudinally extensive, nonenhancing lesions in gray matter of spinal cord; cranial nerve motor nuclei lesions in brainstem; nerve root enhancement later in course	Gadolinium-enhancing, often continguous lesion involving multiple levels of the spinal cord; gray and white matter with associated edema	Normal brain and spinal cord imaging; nerve root and cauda equina enhancement common	Multiple poorly defined heterogeneous, bilateral, often asymmetric lesions in the deep white and gray matter; spinal cord involvement possible
	EMG/NCS features	Low response amplitude of CMAPs; reduced recruitment of MUPs;fibrillation potentials;no sensory findings	Abnormal somatosensory evoked potentials and motor evoked potentials	Slowed nerve conduction velocities reflecting segmental demyelination and absent H reflexes early in course; Motor units with denervation potentials common by 3 weeks; normal sensory potentials in acute motor axonal neuropathy variant	Typically none
Treatment/ course	Response to treatment	No response noted to IVIG, steroids, PLEX	Response to high-dose IV steroids, second-line PLEX, IVIG	Response to IVIG, second-line PLEX	Response to high-dose IV steroids, second-line IVIG, or PLEX
	Course	Muscle atrophy in affected limbs;most with functional improvements, but residual limb weakness	Partial recovery in most over months to years; some degree of residual disability in most	Return of function over weeks to months with favorable outcome in most	Most improve with treatment though with incomplete recovery
	Recurrence risk	No recurrences have been reported to date	A subset will eventually develop a relapsing autoimmune condition (eg, MS, NMO).	Typically monophasic, although chronic, relapsing disease may develop in ~2% of individuals.	Monophasic in >80% of cases

CSF = cerebrospinal fluid; EMG = electromyography; NCV = nerve conduction velocity; CMAPs = compound muscle action potentials; MUPs = motor unit potentials; IVIG = intravenous immunoglobulin; PLEX = plasmapheresis; IV = intravenous; MS = multiple sclerosis; NMO = neuromyelitis optica.