diagnosing CTS and ulnar neuropathy with PPN

[PMR 4 MSK]

I get a fair amount of pt's in for carpal tunnel screens who also have peripheral polyneuropathy (PPN) on EDx, many of whom do have CTS. Many of these have reduced NCV in the forearm of the median and ulnar nerves, as well as the ulnar across the elbow. I'm hesitant to call it a superimposed cubital tunnel syndrome, especilly when the needle exam is benign.

Also, a number of them have delays of both the median and ulnar nerves across the wrists. Again, I am hesitant to call it Guyon's canal syndrome.

Any thoughts on when you call ulnar neuropathy in PPN?

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[Ludicolo]

I think you hedge. For a unilateral mononeuropathy superimposed on a generalized PN – helps if you can demonstrate a significant asymmetry side-to-side. If all distal latencies are prolonged, you could use latency differences (i.e. median/ulnar palmar sensory comparisons) to further evaluate for superimposed CTS. If the PN is severe enough, you just might not be able to make any decisions.

The phrase “clinical correlation is recommended” is your friend.

 

[ben3133]

To add to what Ludicolo said..

For Guyon's canal - you could check dorsal ulnar sensory latency and see how it compares to palmar.

For cubital tunnel - could you call it cubital tunnel if CV above->below elbow is >=8m/s more than wrist->above elbow..? Because in PN you get distal fallout first, if proximal is more affected than distal you could consider a superimposed pathology.

 

[Ludicolo]

To add to what Ludicolo said..

For Guyon's canal - you could check dorsal ulnar sensory latency and see how it compares to palmar.

For cubital tunnel - could you call it cubital tunnel if CV above->below elbow is >=8mV more than wrist->above elbow..? Because in PN you get distal fallout first, if proximal is more affected than distal you could consider a superimposed pathology.

Watch your units

Yes, one of the criteria for ulnar neuropathy at the elbow is focal slowing: i.e. CV aboveàbelow elbow is >= 8m/s slower than CV below elbowàwrist. You might be able to use this if you assume an underlying mild, pure axonal polyneuropathy. Bets are off with a demyelinating or a more severe neuropathy. I still think that your argument is best strengthened if you can document asymmetry.

Alternatively, you could always inch across the elbow or wrist, if you’re into that sort of thing.

 

[ben3133]

Oops thanks for the correction!

That's a good point about the severity/nature of the neuropathy - and shows why it's so important to look for asymmetry.

 

[PMR 4 MSK]

To add to what Ludicolo said..

For Guyon's canal - you could check dorsal ulnar sensory latency and see how it compares to palmar.

For cubital tunnel - could you call it cubital tunnel if CV above->below elbow is >=8m/s more than wrist->above elbow..? Because in PN you get distal fallout first, if proximal is more affected than distal you could consider a superimposed pathology.

Watch your units

Yes, one of the criteria for ulnar neuropathy at the elbow is focal slowing: i.e. CV aboveàbelow elbow is >= 8m/s slower than CV below elbowàwrist. You might be able to use this if you assume an underlying mild, pure axonal polyneuropathy. Bets are off with a demyelinating or a more severe neuropathy. I still think that your argument is best strengthened if you can document asymmetry.

Alternatively, you could always inch across the elbow or wrist, if you’re into that sort of thing.

I find the problem is in interpreting in the case of more cevere axonal PPN. In demylinating PPN , I won't call entrapment, or the surgeon will try to cut on 'em.

I've done a lot of inching and find that when the NCV is in the lower 40's, you get borderline to slightly increased deltas throughout the nerve, or patchy, like 4-5 segments in a row.

I just hate hedging, makes me feel like a radiologist.