two atypical radic studies

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topwise

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I hope this isn't too basic for the people here. I'm still just learning though and this one stumped me. And my attending couldn't offer me an answer that satisfied me.

So I had two patients, both CTS v cervical radic work-ups. Both had bilateral symptoms, mostly sensory, but we only did EMG on one side. I won't get into the whole history until you want me to, but basically:

Patient #1: NCS normal except for median motor decreased amplitude ONLY on the more symptomatic side (distal latency borderline normal bilaterally). The waveform for the median motor was also biphasic, which got a little better when I moved the active electrode but I couldn't get rid of it. All sensory studies normal bilaterally (did ulnar as a comparison). EMG totally negative.

Patient #2: NCS normal except for median motor with significantly increased distal latency only on the more symptomatic side (~125% of normal), but with normal amplitude. Sensory studies all normal as above. The exam was technically difficult though and an extremely large stimulus had to be used due to the patient being obese with a lot of edema. EMG showed fibs and PSWs in all C6 innervated muscles we tested, but paraspinals neg.

I rarely see abnormal median CMAPs in the face of normal SNAPs, let alone two in one day. In the second patient, I wanted to explain the abnormal CMAP as part of the radic, but wouldn't that cause decreased amplitude instead of prolonged latency? I've read that pure median motor mononeuropathies are rare, so how can you explain these two cases?

Sorry in advance if this is a stupid question.

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1. Possibly technical. Was the cmap decreased both proximally and distally, what % between the two? If it is just a distal phenomenon, you may have overstimulated and picked up some ulnar in your waveform.

2. This needs to be correlated with physical examination. From the information you provide sounds like motor median neuropathy (at the wrist), remember CTS is a clinical diagnosis, with a concomitant radiculopathy.
 
1. The amplitude both proximally and distally was about 1/3 of the contralateral side.

2. The reason I questioned a concomitant CTS diagnosis based on these values is that the NCS abnormal values were ONLY motor. Isn't that fairly unusual in CTS?
 
Were there MUP changes or fibs in OP?

Sometimes the motor branch to the thenar eminence can exit the flexor retinaculum through a separate foramen to the sensory branch and thus be affected to a different extent. Alternatively, if there is thenar wasting then that could explain the reduced amplitude.
 
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