Misinterpretation of sural nerve conduction studies due to anatomical variation
Introduction
Nerve conduction studies are important diagnostic tools to evaluate the integrity and function of the peripheral nervous system. The sural nerve is one of the most commonly examined nerves by nerve conduction studies, mainly for the diagnosis of polyneuropathy, but it is also useful in the evaluation of focal nerve injury of the lumbosacral plexus and the sciatic and tibial nerves.
The sural nerve is traditionally described by three different formation types, designated A, B, and C (Huelke, 1957). Type A, the most common type, is formed by the union between the medial sural cutaneous nerve (MSCN), which is a branch of the tibial nerve, and the peroneal communicating branch (PCB) of the common peroneal nerve, while type B is the direct continuation of the MSCN with the PCB absent, and type C is formed by the PCB only (Fig. 1). The union in type A may take place anywhere between the popliteal fossa and the lateral malleolus. Numerous cadaver studies have been conducted worldwide documenting the anatomical variations of the sural nerve (Eid and Hegazy, 2011, Huelke, 1957, Madhavi et al., 2005, Mahakkanukrauh and Chomsung, 2002, Pyun and Kwon, 2008, Shankar et al., 2010). In one of these, sural nerve conduction studies from healthy adults were done in addition to the cadaver studies showing highly variable sural nerve formation (Pyun and Kwon, 2008). Recently, an ultrasound study of anatomic variants of the sural nerve has shown similar variations as the cadaver studies (Zhu et al., 2011). These studies have mainly focused on surgical implications such as reconstruction of peripheral nerves, since the sural nerve is commonly used for nerve biopsies as well as a convenient source for nerve grafting.
From a neurophysiological point of view, the type A with a very distal union between MSCN and PCB as well as type C can cause problems, while type A with proximal union and type B show similar nerve conduction studies, probably without giving rise to any technical problems. However, despite the fact that the variability in the formation of the sural nerve may affect the parameters of sural nerve conduction studies, neurophysiologists have in general not paid much attention to the anatomical variation. In this study, we present 17 subjects with anatomical variation of the sural nerve examined electrophysiologically with both surface electrodes and near-nerve needle technique.
Section snippets
Material
We examined prospectively 240 consecutive subjects referred on suspicion of polyneuropathy. In all subjects bilateral motor conduction studies in the peroneal and tibial nerves and sensory conduction studies in the sural nerve were performed. The median and ulnar nerves were examined on one side in subjects with either electrophysiological changes in the lower extremities or symptoms in the upper extremities. Surface electrode recording was used for motor conduction studies, while sensory
Methods
The sural nerve was further examined in the 17 subjects with a suspected anatomical variation of the sural nerve in order to exclude pathology of the nerve and confirm the variation and identify its type. These supplementing examinations comprised antidromic surface recordings (Falck et al., 1994) and orthodromic near-nerve needle recordings with both the one-threshold (Behse and Buchthal, 1971, Buchthal and Rosenfalck, 1966, Rosenfalck and Rosenfalck, 1975, Trojaborg, 1992) and the two-
Type A formation
A type A formation with distal union of MSCN and PCB was found in 15 subjects. With orthodromic near-nerve two-threshold recording at mid calf at the lateral edge of the Achilles tendon, the SNAP amplitude was decreased bilaterally in 2 subjects and unilaterally in 13 subjects; right-sided in 6 and left-sided in 7. Of the subjects with unilateral variation, 9 had decreased SNAP amplitude at one side, while in 4 subjects the sural SNAP amplitudes were within normal ranges but showed an asymmetry
Discussion
In this study an anatomical variation instead of pathology of the sural nerve was confirmed in 17 out of 118 subjects (14.4%) with no neurophysiological evidence of polyneuropathy. A type A formation with union of MSCN and PCB at the low calf distal to the electrode placement 12.5 cm above the lateral malleolus was found in 15 subjects, while a type C formation of the sural nerve was found in 2. The variation was bilateral in both subjects with type C formation and in 2 subjects with type A
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Cited by (20)
Reply to “Conduction studies on the sural nerve”
2022, Clinical Neurophysiology PracticeElectrodiagnostic Assessment of Polyneuropathy
2021, Neurologic ClinicsCitation Excerpt :Sensory NCS are particularly prone to technical and interpretative errors. Owing to their low amplitude (microvolts), anatomic variation among individuals and susceptibility to technical and age-related factors, lower limb SNAPs may be difficult to obtain and absent responses without clinical correlation should be interpreted with caution.9,10 In addition, background noise and random baseline variations should not be mistaken for “true” SNAPs and averaging of several traces is recommended to demonstrate accuracy and consistency of the responses.10
Anatomy of the sural nerve complex: Unaccounted anatomic variations and morphometric data
2021, Annals of AnatomyCitation Excerpt :It is also of particular importance in the diagnosis of neuropathies. Those unaware of anatomic variations within this nerve may cause misdiagnosis and misinterpretation of sural sensory nerve action potential amplitudes in diagnostic nerve conduction studies (Tankisi et al., 2014). In the clinical setting, a SN block is used to rapidly anesthetize the lower extremities during surgical repair, in diagnostic and operative procedures, and in trauma (Salam, 2004).
Muscle velocity recovery cycles in neurogenic muscles
2019, Clinical NeurophysiologyCitation Excerpt :Sensory NCS was performed either by near nerve recordings or surface electrode techniques. With near-nerve needle technique, the superficial peroneal nerve was stimulated by supramaximal stimulation at retinaculum superior and sensory nerve action potentials (SNAPs) were recorded orthodromically below capitulum fibulae and in fossa poplitea using needle electrodes placed close to the nerve (Tankisi et al., 2014). With surface electrode technique, the superficial peroneal nerve was stimulated at lateral crus and SNAPs were recorded at retinaculum superior.
Diagnostic utility of distal nerve conduction studies and sural near-nerve needle recording in polyneuropathy
2017, Clinical NeurophysiologyCitation Excerpt :As described elsewhere, the amplitude was measured peak-to-peak and the latency was calculated from the stimulus onset to the first positive peak for determination of conduction velocity (CV) (Falck et al., 1994). Insulated needles (0.7-mm diameter) with a 3-mm bared tip were inserted close to the sural nerve at the lateral malleolus for supramaximal stimulation, and at mid calf 12–13 cm proximal to the lateral malleolus for orthodromic SNAP recording (Tankisi et al., 2014). The reference electrode had a 5-mm bared tip and was inserted 2.5–3.5 cm crosswise at mid-calf and lengthwise at the lateral malleolus.
Anatomical variations of the formation and course of the sural nerve: A systematic review and meta-analysis
2015, Annals of AnatomyCitation Excerpt :Furthermore, SN grafts have been shown to have good long term viability, producing satisfactory clinical results in patients undergoing complicated procedures, such as open radical prostatectomy and axillary nerve reconstruction (Aktan Ikiz et al., 2005; Moor et al., 2010). Awareness of the anatomical variations of the SN is important to avoid misinterpretations of nerve conduction studies (Tankisi et al., 2014). In a study by Tankisi et al. (2014), 17 out of 240 patients had anatomical variations of the SN which affected the nerve conduction study performed for the diagnosis of polyneuropathy.