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Viral Myelitis


KEY FACTS

Terminology

  • Acute inflammatory insult of spinal cord due to direct viral infection or postviral immunologic attack

Imaging

  • Swollen, edematous spinal cord with segmental contiguous involvement

    • From 1 segment to extensive cord involvement

  • Fusiform expansion of spinal cord

  • Diffuse increase in T2 signal intensity through involved segment

  • Variable, patchy enhancement of involved cord segment

Top Differential Diagnoses

  • “Idiopathic” transverse myelitis

  • Multiple sclerosis

    • Most lesions are focal (1-2 segments), may be multiple

    • Acute lesions exhibit focal enhancement with short segment edema

  • Acute cord infarct

    • Acute stroke-like presentation

    • Motor signs predominate

  • Neuromyelitis optica

Pathology

  • Since near complete eradication of polio, other enteroviruses most common etiology

  • Edematous, boggy cord ± necrosis

Clinical Issues

  • Acute onset of weakness following febrile illness or upper respiratory tract infection

  • Cerebrospinal fluid shows elevated mononuclear counts and protein level

  • Principal treatment supportive with antiviral drugs ± steroids, variable efficacy

Diagnostic Checklist

  • Strong diagnostic clue in patients with acute onset of myelopathy: Long, segmental cord enlargement and edema without focal lesions

Sagittal T2WI MR shows hyperintensity in the distal thoracic cord and conus
in this patient with West Nile virus (WNV), confirmed with positive IgM serology. WNV can cause meningitis, encephalitis, ± an irreversible acute flaccid paralysis. WNV shows a predilection for the deep gray nuclei in the brain and the spinal cord.

Axial T2WI MR in the same patient with WNV demonstrates hyperintensity in the distal thoracic cord central gray matter
.

Sagittal T1WI C+ FS MR displays enhancement along the distal cord and cauda equina
due to WNV. This patient had a poliomyelitis-like syndrome.

Axial T1WI C+ MR of the same patient illustrates linear enhancement of the cauda equina
. Most WNV-associated acute flaccid paralysis is due to spinal motor neuron involvement producing an anterior myelitis.

TERMINOLOGY

Abbreviations

  • Acute transverse myelitis (ATM)

Definitions

  • Acute inflammatory insult of spinal cord due to direct viral infection or postviral immunologic attack

IMAGING

General Features

  • Best diagnostic clue

    • Swollen, edematous spinal cord with segmental contiguous involvement

  • Location

    • Cervical, thoracic segments; isolated conus involvement rare

  • Size

    • From 1 segment to extensive cord involvement

  • Morphology

    • Fusiform expansion of spinal cord

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