S1 radiculopathy

Dermatomes according to the Neuroanatomy site http://www.neuroanatomy.wisc.edu/

While we concentrated on the differential of radiculopathy in general and how to work with acute back pain patients for L5 radiculopathy last year, we worked up the gory details of clinical examination, pathophysiology and neurophysiology of S1 radiculopathy today.

Some things I learned:

  • As S1 exits between S1 and S2 (where the disc is not the problem), it usually is affected above the foramen and thus by more proximal lesions, such as a paramedian L5/S1 disc or spinal stenosis.
  • It is quite common and seems to happen without pain more often than L5 – how could you explain the many asymptomatic achilles tendon asymmetries out there?
  • As always in radiculopathy you have to examine all levels around the core region of interest (say L3-S4).

Neurophysiology can help to

  • localize the lesion (if axonal: EMG)
  • differentiate plexopathy and neuropathy from radiculopathy (use sensory nerve conduction times)
  • differentiate between demyelinating (i.e. reversible) and axonal lesions (H-reflex works particularly well for this)
  • pave the way for future neurophys investigations, in particular, if after surgery pain and neurology persists.

I am hard pressed for any references, since all this is pretty much folklore. I use the famous Stöhr/Mumenthaler (partly edited in our house) and also my favorite electric book.


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