Hatice Tankisi1, Kirsten Pugdahl2, Marit Otto2, Anders Fuglsang-Frederiksen2. 1. Department of Clinical Neurophysiology, Aarhus University Hospital, Aarhus, Denmark. Electronic address: hatitank@rm.dk. 2. Department of Clinical Neurophysiology, Aarhus University Hospital, Aarhus, Denmark.
Abstract
OBJECTIVE: Anatomical variation of the sural nerve has been documented in numerous cadaver studies. The sural nerve conduction parameters can potentially be influenced by the sural nerve type A formation formed by the union of the medial sural cutaneous nerve (MSCN) and the peroneal communicating branch (PCB) and the type C formation with the sural nerve formed solely by the PCB. METHODS: In 17 out of 240 prospectively examined subjects referred for polyneuropathy a suspicion of an anatomical variation of the sural nerve was raised due to decreased amplitude or substantial side-to-side variation (>50%) of the sensory nerve action potential (SNAP) in disproportion to the clinical findings. To verify the variation the sural nerve was examined further with surface electrodes and near-nerve technique, including extra lateral and distal needle placements. RESULTS: In all 17 subjects an anatomical variation affecting the sural SNAP was confirmed as a normal sural SNAP could be obtained by changing the electrode placement. The most frequent variation, seen in 15 subjects, was a type A formation with union of the MSCN and the PCB distally at low calf, while a type C formation was seen in 2 subjects. CONCLUSIONS: In case of a decreased sural SNAP amplitude or substantial side-to-side variation in disproportion to the neurologic evaluation, an anatomical variation instead of pathology could be suspected and a different electrode placement be considered. SIGNIFICANCE: Neurophysiologists should be aware of different types of formations of the sural nerve which may cause misinterpretations of nerve conduction studies, especially when needle electrodes are used.
OBJECTIVE: Anatomical variation of the sural nerve has been documented in numerous cadaver studies. The sural nerve conduction parameters can potentially be influenced by the sural nerve type A formation formed by the union of the medial sural cutaneous nerve (MSCN) and the peroneal communicating branch (PCB) and the type C formation with the sural nerve formed solely by the PCB. METHODS: In 17 out of 240 prospectively examined subjects referred for polyneuropathy a suspicion of an anatomical variation of the sural nerve was raised due to decreased amplitude or substantial side-to-side variation (>50%) of the sensory nerve action potential (SNAP) in disproportion to the clinical findings. To verify the variation the sural nerve was examined further with surface electrodes and near-nerve technique, including extra lateral and distal needle placements. RESULTS: In all 17 subjects an anatomical variation affecting the sural SNAP was confirmed as a normal sural SNAP could be obtained by changing the electrode placement. The most frequent variation, seen in 15 subjects, was a type A formation with union of the MSCN and the PCB distally at low calf, while a type C formation was seen in 2 subjects. CONCLUSIONS: In case of a decreased sural SNAP amplitude or substantial side-to-side variation in disproportion to the neurologic evaluation, an anatomical variation instead of pathology could be suspected and a different electrode placement be considered. SIGNIFICANCE: Neurophysiologists should be aware of different types of formations of the sural nerve which may cause misinterpretations of nerve conduction studies, especially when needle electrodes are used.
Authors: Thomas Krøigård; Kjeld V Andersen; Hatice Tankisi; Sándor Beniczky; Alexander Gramm Kristensen Journal: Clin Neurophysiol Pract Date: 2021-12-13