Nerve conduction study results interpretation

Edit: p.2 of NCS - http://tinypic.com/r/n1q7up/9

Those results do not obviously show CTS at all but they do not show the normal ranges for that lab so it's hard to say on what basis they concluded there was evidence of CTS. The problem is that different labs have different ranges of what they consider to be 'normal'. A good lab should really state on their report what they consider to be normal. I think it is fair to say that in most labs those results would be considered normal. The simplest indicator is the median orthodromic sensory conduction velocity which is given as 62 m/sec for the left median nerve and 56.5 m/sec for the right median nerve. This is the speed at which a signal travels along the nerve form the finger to wrist and it slows down in CTS. In my lab anything under 40 m/sec would be clearly abnormal and anything between 40-45 would be reason for suspicion and further testing to confirm the abnormality but 56 is nowhere near those values. I can only assume they are saying this based on the difference between 56 and 62 but there is inherent measurement error in these studies so small side to side differences easily arise by chance. Rather oddly they have gone on to carry out a further test in the right hand, and on that side they have obtained a conduction speed of 54.8 m/sec across the carpal tunnel but apparently they consider that one normal from what you say? It is not unknown, I have to say, for neurophysiologists to ignore the measured results and write a conclusion based on what they think the patient has on other grounds. This is not something I approve of but I have seen it done. If you want to send me the whole eport (email is best) I might be able to comment further. (incidentally there is a bit of ambiguity in your original post about right and left sides - it's not clear which side was reported to be abnormal) JB

Postscript - some of the above should probably be ignored - it was the right hand which was reported abnormal - not the left as in the orignal post so I really did have trouble making sense of these.

Hi Jeremy,

Thanks so much for your long reply. I had meant to say that they diagnosed carpal tunnel in my right hand (rather than left), bu that I experience symptoms more in my right hand than in my left.

Based on the limited amount that I have read, I thought his diagnosis would have bean based on the difference between the peak latency of the median sensory and ulnar sensory nerve on each hand. This difference is 0.65 for the right hand and 0.5 for the left.

I have emailed you a scan of the complete report.

Thanks again

Ok I think I've got the sides right now. It is the right side that has been reported abnormal. The NCS results show slightly slower sensory conduction in the right median nerve - in the region of 55m/sec compared to 61 m/sec in the right ulnar nerve and 62 m/sec in the left median nerve so the right median nerve is about 6 or 7 m/sec slower than the nerves it is being compared with. I guess that must fall outside the normal limits for that lab but we will have to ask the responsible neurophysiologist what their limit is for that sort of comparison. It's not a way of analysing these results that I use personally so I don't have a local normal range of my own for this particular comparison. I prefer to use more direct median/ulnar comparative methods but there are so many valid ways of testing for CTS that almost every lab can devise their own unique methodology and although numerous papers have been published arguing that one method or another is the 'best' in reality there is no way of resolving the argument for good. My rather pragmatic view is that if you are struggling to show an abnormality and having to make very detailed comparisons of median nerve conduction with another nerve then any CTS is too mild to require urgent surgery. One can therefore afford to experiment with less aggressive treatments if you really think that is the right diagnosis. Of the other results the right median sensory potential is a little smaller than the left and the right median distal motor latency is a little later than the left but neither of these differences look significant to me. JB

OK. The neurophysiologist who reported those has confirmed that it is the asymmetry between the two sides and the difference between median and ulnar nerve conduction which is being interpreted as outside the limits of side to side and nerve to nerve comparison for them, though I think he is also taking into consideration the more abnormal results seen on the previous studies and, reading between the lines, I think there is a sense in which the overall conclusion reflects what he thinks about your case overall - not purely an opinion on what the NCS results show.

I'm still a bit unclear about exactly what your symptoms are and which is in fact the more symptomatic side so if you run through the symptom questionnaire on here we might be able to put the NCS results in a better context. JB