Normal motor nerve conduction studies using surface electrode recording from the supraspinatus, infraspinatus, deltoid, and biceps

Abstract

Objective: Proximal peripheral nerve conduction studies can provide useful information to the clinician. The difficulty of measuring the length of the proximal nerve as well as a frequent inability to stimulate at 2 points along the nerve adds a challenge to the use of electrodiagnosis for this purpose. The purpose of this article is to present normal values for the suprascapular, axillary, and musculocutaneous nerves using surface electrodes while accounting for side-to-side variability.

Design: Prospective, observational study.

Setting: Patients were evaluated in outpatient, private practices affiliated with tertiary care systems in the United States and Malaysia.

Participants: One hundred volunteers were recruited and completed bilateral testing. Exclusion criteria included age younger than 18 years; previous shoulder surgery/atrophy; symptoms of numbness, tingling, or abnormal sensations in the upper extremity; peripheral neuropathy; or presence of a cardiac pacemaker.

Methods: Nerve conduction studies to bilateral supraspinatus, infraspinatus, deltoid, and biceps brachii muscles were performed with documented technique. Distal latency, amplitude, and area were recorded. Side-to-side comparisons were made. A mixed linear model was fit to the independent variables of gender, race, body mass index, height, and age with each recorded value.

Main outcome measurements: Distal latency, amplitude, area, and side-to-side variability of nerve conduction studies of the suprascapular, axillary, and musculocutaneous nerves with correlation to significant independent variables.

Results: Data are presented showing normal distal latency, amplitude, and area values subcategorized by clinically significant variables, as well as acceptable side-to-side variability. Increased height correlated with increased distal latency in all the nerves tested. Amplitudes were larger in the infraspinatus recordings from women, while the amplitudes from the biceps and deltoid were greater in men. A larger body mass index was associated with a smaller amplitude in the deltoid in men. No correlations were seen with age or race.

Conclusion: Normative values for distal latency, amplitude, duration, and area were developed for proximal nerve conductions to the axillary, musculocutaneous, and suprascapular nerves. Simple surface electrode placement allows for easy reproduction of the authors' techniques. This is a useful standard to facilitate evaluation of these proximal peripheral nerves.