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e: Suprascapular Nervetudies—Surface Versus Needleickup Electrodes

o the Editor,I compliment Buschbacher et al [1] on detailed studies to

stablish the normal amplitude and latencies for the proximalerve conduction studies in the upper extremity. However, Iave a few objections to the use of surface electrodes for theuprascapular nerve studies.

First, supraspinatus muscle is covered by the trapezius,nd many times it is difficult to pickup contraction occurringn the supraspinatus muscle, especially in obese people orery muscular persons. To some extent the same is true withnfraspinatus in such individuals. Buschbacher et al’s study1] as well as the Casazza et al’s study [2] show that amplitudef response with a surface electrode is very small. Second,uch a small amplitude can be a major problem when there iserve lesion, especially when there is significant atrophy ofhe surpaspinatus muscle.

Third, when we stimulate at the Erb’s point, it is possiblehat a volume conducted response can stimulate the spinalccessory nerve. When there is an entrapment of the surpas-apular nerve, it is possible that stimulus may reach therapezius before it reaches supraspinatus and thereby anrroneous conclusion. Robinson [3] warns that coactivationf nearby muscles can be a problem in the stimulation ofroximal regions of the peripheral nervous system.

Fourth, a suprascapular nerve study requires the practi-ioner to perform a needle examination of the supraspinatu-and infraspinatus. If so, why not use a needle pickup foroth surface stimulation and also to record EMG activity?his does not subject the patient to any additional discom-

ort. With 2-channel nerve conduction pickup, we can gethe response from both muscles simultaneously. We canake sure that the needle is in the right muscle by recordingMG activity before nerve stimulation.

Finally, it appears that Buschbacher et al [1] are notorrectly quoting Casazza et al’s study [2]. In their article inelectromyography and Clinical Neurophysiology, they clearlytate that monopolar needle pickup is more accurate toecord responses from supra and infraspinatus muscles.

George Varghese, MDDepartment of Rehabilitation Medicine

University of Kansas Medical CenterKansas City, KS

G.V. Disclosure: nothing to disclose

DOI: 10.1016/j.pmrj.2009.06.005

M&R © 2009 by the Am934-1482/09/$36.00

rinted in U.S.A.

EFERENCES. Buschbacher RM, Weir SK, Bentley JG, Cottrell E. Normal motor nerve

conduction studies using surface recording from the supraspinatus,infraspinatus, deltoid, and biceps. PM&R 2009;1:101-106.

. Casazza BA, Young JL, Press JP, Heinemann AW. Suprascapular nerveconduction: A comparative analysis in normal subjects. ElectromyogrClin Neurophysiol 1998;38:153-160.

. Robinson L. In discussion of: Patel AT, Robinson L, Akuthota V. Utility ofproximal nerve conduction studies. PM&R 2009;1:278-279.

EPLY:

o the Editor,We appreciate Dr. Varghese’s comments. It is indeed a potential

roblem to use surface recording of a muscle that is covered bynother muscle. In fact, even inadvertent recording from adjacentrdeepmuscles is apotentialpitfall. If the stimulationpoints for thepinal accessory and suprascapular nerves were identical, this tech-ique would not be a feasible one. The 2 stimulation points are,owever, distinct enough that inadvertent spinal accessory nervetimulation was not a problem in our series.

Although the amplitudes recorded were on the small side,hey were not tiny, and the responses, at least in our normalubjects, were easily identified. In case of an atrophic muscle itould seem that surface recording would be particularly useful,

specially using a side-by-side comparison. Testing only oneide in a large individual might be difficult to interpret, but anilateral decrease in amplitude would be of significance. Oneedle recording an atrophic muscle with a fairly normal latencyay not be identified as being abnormal.Most electromyographers would likely agree that sur-

ace recording is preferable to needle recording becauseurface recording allows the interpretation of amplitudes.n cases in which there are problems with this technique,s in other areas of the body, a needle recording can alwayse used to supplement the study. However, in our experi-nce with this series, surface recording would seem to beasy and reliable. Dr. Varghese is correct in pointing out anrroneous reference to the Casazza study, and we regrethe error.

Ralph Buschbacher, MDSusan Weir, MD

Indiana University School of MedicinePhysical Medicine and Rehabilitation

Indianapolis, INR.B. Disclosure: nothing to disclose

S.W. Disclosure: nothing to disclose

DOI: 10.1016/j.pmrj.2009.06.006

erican Academy of Physical Medicine and RehabilitationVol. 1, 785, August 2009 785