carpal tunnel

[topwise]

This isn't exactly a case, but as a resident, I am curious for the opinions of people who do a lot of EMGs in the Real World. If this is not an appropriate post for this forum, I apologize. Hopefully these questions don't sound too naive.

1) In a case of CTS study, if the median motor and sensory studies are normal, what is your next step? Do you go through all three studies to calculate the sensitivity index? Or just one?

2) Is there any definitive way to determine if there is axonal loss with just NCS? (I have heard a lot of conflicting answers on this one so I would love to see a good source.)

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[Disciple]

1. Do the Med/Ulnar palmar study, then Med/Rad, Med/Uln(Dig IV). You can stop at any point if any of these studies individually shows a significant difference in latencies. If not, do the complete combined sensory index.

2. Check your pocket pedia for criteria for Axonal vs Demyelinating based on NCS. There are not hard and fast values/criteria, but you get the basic idea.

 

[SSdoc33]

This isn't exactly a case, but as a resident, I am curious for the opinions of people who do a lot of EMGs in the Real World. If this is not an appropriate post for this forum, I apologize. Hopefully these questions don't sound too naive.

1) In a case of CTS study, if the median motor and sensory studies are normal, what is your next step? Do you go through all three studies to calculate the sensitivity index? Or just one?

2) Is there any definitive way to determine if there is axonal loss with just NCS? (I have heard a lot of conflicting answers on this one so I would love to see a good source.)

1. there's a good article on this by larry robinson that gives you a basic algorithm to minimize tests and maximize results for a CTS study. here's the pubmed link
http://www.ncbi.nlm.nih.gov/pubmed/11102914?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSumhttp://www.ncbi.nlm.nih.gov/pubmed/11102914?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_


you should note that doing a straight median motor to digit 2 would actually add an un-needed sensory study. i usually just do median and ulnar sensory and motor. rarely is another study necessary, as the diagnosis is generally pretty clear. if its iffy, ill do a transcarpal or the whole CSI, but thats rare, tto be honest.


2. while i think you CAN determine axon loss by NCS alone, needle EMG is a more sensitive technique to pick this up. even mild axonal damage should be seen on EMG

 

[axm397]

One of my attendings trained under Larry Robinson and he starts by doing median and ulnar motor (so if motor absent or severly delayed, know not to waste too much time hunting around for median sensory)

then he does median and ulnar sensory to the 4th digit, then median and radial to the thumb (numb thumb), then the palmar studies if necessary (until CSI significant) - which can cut down on the number of studies needed.


He usually does a cervical radic screen with EMGs - because most patients have neck pain. Some of my other attendings will just stop after the NCS.

 

[PMR 4 MSK]

My problem with these approaches is what are you trying to prove? That the patient has a borderline vs very mild CTS? How clinically significant is this? How's it going to change your treatment?

If the comparison of median-to-ulnar doesn't show any difference through standard motor and sensory testing, convince me that doing several more tests doesn't significantly raise the false-postive rate by raising the true-positive rate. When doing these studies, what do you use as the "gold-standard?"

At some point, you make a call based as much on arbitrary cut-offs as science. When we say a difference of 1.0 ms is significant, but 0.9 isn't, that's arbitrary.

Secondly you then have two choices with this, bill 2 motors and 6-8 sensories per limb, which'll get bounced on review by insurance, or spend a lot of time chasing a controversial technique for splitting hairs and then not actually billing for it.

 

[topwise]

Thank you to everyone for your responses. I've done EMGs with half a dozen attendings and they all approach carpal tunnel differently. Like some will go for the combined sensory index even if the basic median motor and sensory are abnormal. Some of them will just do the midpalmar study and stop there, even if it's normal.

As for the axonal loss question, I've had attendings insist either way that you can or cannot tell if you have axonal loss with NCS alone. I don't know what to believe anymore....

 

[Disciple]

Just keep in mind what the person requesting the study wants to know. This will guide what you do.

As alluded to above, you can waste time doing things that aren't necessary e.g. the palmar sensory comparison is for detecting mild Median mononeuropathy. Why do this if the motor and/or Dig II sensory are already abnormal?

Kind of like always doing F-waves on all your motor studies or proving mild CTS and then always sticking someone in the hand (painful).

 

[caedmon]

We start with median ulnar motors. If the median motor is abnormal, then do median to 2nd sensory. If median motor is normal, then do median/ulnar palmor sensories as it's more sensitive.

Agree with PMR 4 MSK that if basic studies are normal, you're probalby not going to change management much (or shouldn't). It's crazy that you see so many symptoms that aren't classic with postive CTS findings, or minimal findings with severe symptoms.

If axonal loss is fairly significant you could probably due MUNEs to see estimate axonal loss. Not sure of the utility in CTS though.

 

[spondy14]

I always start with median and ulnar sensory because cold fingers can set in pretty quick from both a timing and vasoconstriction standpoint. I disagree that I might be wasting my time looking for the median sensory....it is pretty easy to find. Of course if it is not there right away or very small and slow, then you have a pretty good clue that it is going to be CTS. I use palmar orthodromic next and should be the gold standard, and then go into motors to confirm moderate or severe. It is amazing how many different tests get used and how all attendings differ. I think if the palmar difference is .6 or .7, why go on? Even if the other two are normal I would call it (although very mild and is it going to change tx..i agree). If it is normal, how many times have the others been abnormal...I have never seen it, but maybe not looking enough.