Background

• First described 1959
• “juvenile muscular atrophy” of distal upper limb extremity
  or “monomelic amyotrophy.”

Background

• Insidious onset asymmetric wasting distal upper ext
• sparing brachioradialis
• C8-T1
• 2nd-3rd decades (15-25 years old)
• M > F
• RUE > LUE

Materials and Methods

• January 2014 to July 2017, Northeast India
• Young adults weakness/wasting hand/forearm
• motor axonopathy on nerve-conduction studies

Included subjects

• Other etiologies for weakness
• AS of C-spine
• Prior trauma or fixation
• Inability to adequately flex neck

Excluded subjects

45 subjects

Materials and Methods

• 1.5T Magnetom Avanto (Siemens)
• Imaged c-spine in neutral and flexed position
  • Flexion imaging with body coil
  • 30-40°
  • Post-gad sag and axial in flexed position

MR protocol

Materials and Methods

• Cord flattening, T2 signal, atrophy
• Max forward shift of posterior dura (laminodural space)
• AP + TV diameter of cord in neutral and flexed
• AP diameter of canal in neutral and flexed

Image analysis

Results

• 44 male, 1 female
• 14 - 42 years at presentation, mean 23 years
• 89% unilateral, 11% bilateral
• 100% hand, 60% forearm, 4% arm muscles

Subjects

Results

• localized lower cervical cord atrophy: 60%
  • < 2 vertebral heights in 42%, 2-3 in 11%, > 3 in 7%
  • Max mean atrophy at C6-7
  • asymmetric flattening in 69%

Imaging findings

Results

• T2 cord signal abnormality: 36%
  • Anterior horns: 33%
    • Unilateral: 24%
    • Bilateral: 9%

Imaging findings

Results

Imaging findings

fig. 3

• Loss of dural attachment, forward shifting of posterior dura, enhancing prominent posterior epidural space: 100%

Results

Imaging findings

fig 1

Results

Imaging findings

fig 2

Results

• Max LDS: 3 - 10mm, mean 6mm
• Posterior epidural flow voids: 47%
• Most had increased LDS at both C & T spine
• Diameter of bony canal not sig changed
• At max compression site, cord flattened in AP dimension by avg of 0.7mm
• Mean decrease in AP/TR ratio of 0.12

Imaging findings

Results

Imaging findings

Results

figs. 4, 5, 6

Discussion

Etiology...

• Repeated/sustained flexion leads to necrosis of anterior horn cells 2/2 chronic changes in ASA territory microvasculature
• Differential growth of vert column and cord -> abutment of cord -> ASA ischemia
• ? atopy/immunologic contribution
• Posterior epidural venous engorgement 2/2 impaired venous return from neg pressure in LDS

Discussion

Imaging important in diagnosis

• Neutral MRI may show atrophy, T2 signal, asymmetric flattening
• Flexion MRI shows classic findings
  • Posterior dural detachment -> widened LDS
  • Enh of engorged posterior epidural venous plexus
  • Compression of cord

Discussion

What criteria to use?

• Lehman et al 2013: Sens similar for neutral and flexion (70% vs 71%), but neutral findings subtle

Discussion

What criteria to use

Lehman et al

Discussion

What criteria to use?

• Chen et al 2004: Loss of attachment 93% sensitive
• Lai et al 2011: LDS increase in 46% healthy subjects
  • Proposed BOTH:
    • increased LDS/canal diameter ratio
    • decreased AP/TR cord diameter ratio
  • But only 3 patients 

Discussion

What criteria to use?

• Current study applied these proposed criteria to 45 patients
  • Mean LDS/canal ratio increase: 0.46
  • Mean AP/TR cord diameter decrease: 0.12

Limitations

• No control group to determine cutoff for diagnosing HD
• Uniform neck flexion angle not achieved in all patients

Thoughts

• Ratios of LDS/canal & AP/TV seems like overkill
  • Why not just loss of attachment and decreased AP cord diameter in flexion?
• Flexion images clearly helpful
• Comparison with asymptomatic controls would be helpful