This is a short clinical vignette focusing on ultrasound of the median nerve. A 33-year-old secretary presents to the EMG lab with numbness and tingling throughout her hand, worse on the right. She notices this with typing mostly, but it can wake her at night. She's otherwise healthy. She does have a positive valence test on examination, but otherwise there's no findings of note. Her nerve conduction studies are notable for normal median and ulnar motor responses and also normal median and ulnar sensory responses. We used a Palmer technique, which is orthodromic, and include looking for a relative difference in latency between the median and ulnar, and these were normal. Needle EMG of C5 through T1 innervated muscles was also normal, but given this clinical presentation where it sounded quite strongly as if she may have carpal tunnel syndrome, we decided to proceed with ultrasound. So the first image shows the median nerve at the wrist. This is the nerve here. We measure it just inside that hyper-echoic border, and then we also measure it here in the forearm, and again inside that hyper-echoic border. This is the flexor digitorum superficialis muscle, and then deep to the nerve is flexor digitorum profundus, so it's usually quite easy to see here in the forearm. So at the wrist, the cross-sectional area of the median nerve was 11, which is actually normal in our lab, anything under 12 square millimeters. At the forearm, the cross-sectional area of the median nerve was 5 square millimeters. There was normal mobility of the nerve when she made a fist, the echotextra looked okay, and there was no increased vascularity when we put Doppler on at the wrist. We also looked at the nerve in long axis, and it was normal, there was no evidence of a notch sign or any other compression. So we have a median nerve cross-sectional area at the wrist that is within normal limits, but the wrist-forearm ratio is actually enlarged at 2.2. Our lab has a normal value of 2 or less, well, if the ratio is greater than 2, then that's abnormal. So based on this, we were able to say that despite the normal electrophysiologic study, the findings on ultrasound are consistent with the clinical diagnosis of carpal tunnel syndrome. So the additional use of ultrasound was very helpful in this case.

clinical vignette

numbness and tingling

hand

EMG lab

carpal tunnel syndrome

CTS