Transverse myelitis

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.

Epidemiology

ATM affects 1 - 4 new cases per million people per year ⁷. It affects individuals of all ages with peaks between 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 / 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 (biopsy of the spinal cord has a high morbidity) and 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. These are :

• inclusion criteria:
  • development of sensory, motor, or autonomic dysfunction attributable to the spinal cord
  • bilateral signs and/or symptoms (though not necessarily symmetric)
  • clearly defined sensory level
  • exclusion of extraaxial 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 AVM
• 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 a likely aetiology is present, which include: 

1. idiopathic
2. secondary 
   • acute infection (most commonly viral)
   • post-infection (ADEM(ADEM)
   • post-vaccination
   • autoimmune (SLE(SLE, MS)
   • systemic malignancy

Radiographic features

Lesions may occur anywhere within the cord, however the thoracic cord is 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 ATM.

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 generally 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