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Ultrasound-guided needle positioning in sensory nerve conduction study of the sural nerve
Christian P Kamm1, Olivier Scheidegger, Kai M Rösler
1Department of Neurology, Inselspital, Bern University Hospital, and University of Bern, Switzerland. christian.kamm@insel.ch
Objectives:
To evaluate the usefulness of ultrasound imaging to improve the positioning of the recording needle for nerve conduction studies (NCS) of the sural nerve.
Methods:
Orthodromic NCS of the sural nerve was performed in 44 consecutive patients evaluated for polyneuropathy. Ultrasound-guided needle positioning (USNP) was compared to conventional "blind" needle positioning (BNP), electrically guided needle positioning (EGNP), and to recordings with surface electrodes (SFN).
Results:
The mean distance between the needle tip and the nerve was 1.1 mm with USNP compared to 5.1 mm with BNP (p<0.0001). The mean amplitude of the sensory nerve action potential (SNAP) was 21 microV with USNP and 11 microV with BNP (p<0.0001). Compared to BNP, nerve-needle distances and SNAP amplitudes did not improve with EGNP. SNAP amplitudes recorded with SFN were significantly smaller than with BNP, EGNP and USNP.
Conclusion:
Ultrasound increases the precision of needle positioning markedly, compared to conventional methods. The amplitude of the recorded SNAP is usually clearly greater using USNP. In addition, USNP is faster, less painful and less dependent on the patient.
Significance:
USNP is superior to BNP, EGNP, and SFN in accurate measurement of SNAP amplitude. It has a potential use in the routine near-nerve needle sensory NCS of pure sensory nerves.
