Acute transverse myelitis (ATM) is an inflammatory condition affecting both halves
of the spinal cord and associated with rapidly progressive motor, sensory, and
autonomic dysfunction.
It is mostly imaged with MRI, which generally shows a long segment (3-4 segments or
more) of T2 increased signal occupying greater than two-thirds of the cross-
sectional area of the cord, with variable pattern of enhancement and no diffusion
restriction.
Epidemiology
The incidence of acute transverse myelitis is 1-4 new cases per million people per
year 7. It affects individuals of all ages with peaks at ages 10-19 years and 30-39
years 7. There is no sex or familial predisposition and usually no prior history of
neurologic abnormality.
Clinical presentation
The clinical course is highly variable but typically evolves over hours or days.
Symptoms and signs are bilateral and include:
para- or tetraparesis
sensory impairment level
sphincter dysfunction
Diagnostic criteria
As the diagnosis does not have a sensitive and specific laboratory test, histology
is usually not obtained, particularly as biopsy of the spinal cord has a high
morbidity. Imaging features overlap with other inflammatory and neoplastic
entities. A set of diagnostic criteria have been proposed by the Transverse
Myelitis Consortium Working Group 7:
inclusion criteria
development of sensory, motor, or autonomic dysfunction attributable to the spinal
cord
bilateral signs and symptoms (though not necessarily symmetric)
clearly defined sensory level
exclusion of extra-axial compressive cause by neuroimaging (MRI or myelography; CT
is not adequate)
inflammation within the spinal cord demonstrated by CSF pleocytosis or increased
IgG index or gadolinium enhancement
progression to nadir between 4 hours and 21 days after the onset of symptoms
exclusion criteria
radiation to the spine within the last 10 years
arterial distribution clinical deficit consistent with thrombosis of the anterior
spinal artery
abnormal flow voids on the surface of the spinal cord consistent with AVF
exclusion criteria for idiopathic ATM
connective tissue disease
CNS infection
brain MRI abnormalities suggestive of multiple sclerosis
history of clinically apparent optic neuritis
Pathology
Pathology may reveal perivascular lymphocytic infiltrates, necrosis, and
demyelination. In many cases, no underlying cause is identified. In some patients,
however, an aetiology is identified:
acute infection (most commonly viral)
post-infection (ADEM)
post-vaccination
autoimmune (SLE, MS)
systemic malignancy
Radiographic features
Lesions may occur anywhere within the cord, with the thoracic cord being the most
frequently involved site.
CT
variable enlargement of the spinal cord
variable contrast enhancement patterns (including no enhancement)
MRI
Up to 40% of cases have no findings on MRI 8. In the remainder, the appearance is
variable and non-specific:
there is a large variation in lesion size, however, they most commonly extend for
3-4 spinal segments 3
lesions typically occupy greater than two-thirds of the cross-sectional area of the
cord 3
there is variable enlargement of the spinal cord
Typical signal characteristics include:
T1: isointense or hypointense
T2: poorly delineated hyperintense signal
T1 C+ (Gd): variable enhancement patterns (none, diffuse, patchy, peripheral)
Treatment and prognosis
Treatment of secondary ATM depends on the underlying cause. No treatment currently
exists for idiopathic cases.
One-third of patients recover with little or no sequelae, one-third are left with a
moderate degree of permanent disability, and one-third are left with severe
disabilities 3.
Differential diagnosis
General imaging differential considerations include:
multiple sclerosis
plaques are shorter than two vertebral body segments in length and involve less
than half the cross-sectional area of the cord
plaques are characteristically peripherally located in the dorsal and lateral
columns
in most patients, additional lesions of variable enhancement are present in the
brain and spinal cord (MS is solely confined to the spinal cord in 5-24% of
patients)
ATM can be the presenting feature of MS: 83% of patients with transverse myelitis
who also have lesions on MRI brain will ultimately be diagnosed with MS. If MRI
brain is normal, there is an 11% chance of ultimately being diagnosed with MS 7
ADEM
similar appearance to spinal MS plaques (however younger age at presentation,
monophasic clinical course and more often associated with thalamic lesions)
spinal cord infarct
spinal cord is usually enlarged
hyperintense on T2 weighted images and DWI
post-contrast enhancement may or may not be present (enhancement is usually present
in the subacute stage)
signal intensity abnormality may be limited to the central grey matter or may
involve most of the cross-sectional area of the cord
signal abnormality typically extends over multiple vertebral body segments
can occur at any location in the cord but has a propensity for the upper thoracic
or thoracolumbar regions
vertebral body T2 hyperintensity may occasionally be seen (due to concomitant
infarction)
intramedullary neoplasm
invariable spinal cord expansion
the majority show at least some contrast enhancement
commonly associated with cysts and syringohydromyelia
may have evidence of prior haemorrhage
slowly progressive clinical course
