My legs don’t work – part 2


Is this a “central” or “peripheral” problem? What helps you decide?

This is a central problem. The main clue in the story is the disturbance of bladder function. This is more likely in lesions of the central nervous system.

The examination demonstrates spasticity (increased tone; brisk reflexes, clonus, extensor plantars) and “pyramidal” weakness (flexors weaker than extensors in the legs)

Where is the problem most likely to be?

Spinal cord has to be top of the list. If you said cauda equina, then shame on you (but you’d be closer than the referring team in real life!). Cauda equina causes floppy feet, numb bum and incontinence. Proximal leg weakness has to be in the spinal cord, which terminates at L1.

You could be forgiven for localising this to the thoracic spinal cord but, as it turned out, the lesion was much higher.

What are the top 3 potential causes?

Depends a bit on the rapidity of onset.

  • Onset in seconds/minutes = vascular (arterial occlusion; venous infarction; AV fistula etc.) until proven otherwise
  • Onset in days/weeks = inflammatory, neoplasm, infection
  • Onset in months = degenerative, neoplasm

A good way to approach the spinal cord is to split your differential into extrinsic lesions (outside the cord) and intrinsic lesions (inside the cord). You can then apply a surgical sieve (although I might re-appropriate it as a neurological sieve, given how often I use one).

  • V – ascular
  • I – nfectious
  • T – rauma
  • A – utoimmune
  • M – etabolic
  • I – nflammatory
  • N – eoplastic
  • D – degenerative & drugs
  • E – endocrine
  • C – ongential

When in doubt, sieve it out!

In this case, the diagnosis was of an intrinsic, inflammatory cervical cord lesion. We call this “transverse myelitis” and, in some cases, it is a first presentation of MS. There are lots of other reasons for this too, but we’ll not bore you with them today.

If you had only one test you could do, what would it be?

I hope most of you went for a scan of the spinal cord. If not, visit this lecture.

Those of you who wanted a scan of the lumbar-sacral spine … close, but no cigar. This is too low to find the problem. If you went for the thoracic cord … one pat on the back. If you fancied a scan of the cervical and thoracic cord … many, many pats on the back. Well done!

The spinal cord is tricky and, if you had to take home only one message from this case, it would be this …

You can never scan high enough in a spinal cord problem, but you can always scan too low

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