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Partial Sensory conduction block or temporal dispersion
I am sure this is not the first time this question comes up and it won't be the last time.
33 yo female (very thin) hospitalized six months ago for unrelated illness ( brainstem meningeoma). She had to have PICC line placement through left arm. Allegedly, the needle hit some nerve in the mid medial arm. Now she came for nerve study for a small mass in the same area she had the needle. It is painful to touch. There is sometimes shooting pain down the medial elbow to the anterior medial forearm.
on exam, there is a small (2-3 mm approximately ) round subcutaneous mass, 10 cm proximal to the elbow crease and anterior to the mid axillary line. Tender with no Tinel's sign. Pinprick sensory is basically normal in this arm and forearm.
Suspected partial laceration of left medial antebrachial cutaneous nerve with neuroma formation.
Routine NCS/EMG done. Normal median, ulnar sensory motor studies. Normal needle EMG left UE muscles.
Here comes the question: left medial antebrachial sensory study. Conventional setup. Recording at 10cm distal to the elbow crease on the anterior medial forearm. Stimulation (stimulation "d" for distal to the mass) at 4cm proximal to the crease (14cm in total). This places the stimulation "d" distal to the mass of in question. Second stimulation (stimulation "p" for proximal to the mass) was done 8cm proximal to the stimulation "d".
There is 65% amplitude drop comparing proximal SNAP to distal SNAP respond. Is this normal temporal dispersion or partial conduction block? Considering the fact of 8 cm separation between the proximal and distal stimulations.
thank you. Perhaps, you will ask me to do a contral lateral comparison study. Why?
thank you
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