S164. A novel technique of axillary nerve motor conduction study

Abstract

Introduction Axillary nerve involvement can commonly occur as part of the brachial plexus lesion. In traumatic pathology, the decision to surgically repair the plexus is based on the amplitude of compound muscle action potential. Our aim is to describe a novel technique for axillary nerve motor conduction studies and provide normative data of compound muscle action potential. Methods The active electrode was positioned over the most prominent portion of the middle deltoid, approximately 5–7 cm distal to the acromion. The reference electrode was positioned over the acromion. The ground electrode was placed between the active and the reference electrodes. Supra-maximal stimulation was at the Erb’s point. Routine motor conduction study filters were used to record the CMAP. Study was performed using commercially available ambu stick on electrodes. The recording were performed using Synergy or Viking EMG system. Data was collected from all consecutive patients with axillary nerve palsy referred for suspected brachial plexopathy. The study was performed bilaterally in all patients and the NCS from the asymptomatic side are used to establish the normal values. Patients with bilateral plexus lesion and generalised weakness caused due to peripheral nervous system pathology are excluded from the study. Active electrode was positioned over the most prominent portion of the middle deltoid, approximately 5–7 cm distal to the acromion. Reference electrode was positioned over the acromion. Ground electrode was placed between the active and the reference electrodes. Supramaximal stimulation was at the Erb’s point. Onset-to-peak compound motor action potential (CMAP) and onset latency (OL) were obtained. Statistical analysis was performed using SPSS. Comparison of age sex as a variable factor was done to CMAP and On-set Latency. Results A total of 163 participants (59.5% male) were examined. The ages ranged from 18 to 84 years (mean 50.0 ± 15.8 years). Comparisons between males and females showed no statistically significant differences regarding age (49.6 ± 16.2 versus 50.5 ± 15.4 respectively, p = 0.742). However, males showed significantly higher CMAP in comparison to females (12.8 ± 3.6 versus 11.3 ± 3.5 mV, p = 0.001) and significantly prolonged OL (3.3 ± 0.9 versus 2.8 ± 0.5 ms, p = 0.001). There was a significant positive correlation between the subjects’ age and the OL (Spearman’s rho 0.311, p < 0.001) and a significant negative correlation between the participants’ age and the CMAP (Spearman’s rho −0.472, p < 0.001). Conclusion To our knowledge this is the largest study to-date providing normative data and new easy to perform technique of axillary motor conduction study.