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Ann Thorac Surg 1999;67:291-292
© 1999 The Society of Thoracic Surgeons
a Thoracic, Cardiac and Vascular Surgery, 1201 Barnett Tower, 3600 Gaston Ave, Dallas, TX 75246, USA
To the Editor
Regarding the letter from Wilbourn and Cherington about our recent report [1], we did not recommend performing median nerve conduction studies to diagnose "upper plexus" thoracic outlet syndromes (TOS) (as the letter states). All patients with the upper plexus TOS were diagnosed clinically by two or more physicians before any nerve conduction study measurements. Each patient was diagnosed clinically with regard to having C6 or C7 symptoms, a combination of C6 to C7 and C8 symptoms, or the C8 symptoms alone. The designation of the "upper" and "lower" plexus is that arbitrarily defined by Swank and Simeone [2] and later by Sanders [3] and Wood and colleagues [4]. The designation of upper and lower plexus is primarily a clinical diagnosis. The conduction studies simply corroborated the clinical diagnosis.
The purpose of our report was to refute the necessity of two operations, a supraclavicular and transaxillary for upper plexus symptoms. It was clinically demonstrated that a single operation through the transaxillary route treated the patients with upper plexus as well as those with lower plexus TOS compression [5].
The letter by Wilbourn and Cherington states:
if motor slowing across the thoracic outlet occurs with TOS, slowing should be found on both the median and ulnar nerve conduction studies with the "lower plexus" type TOS and undetected by nerve conduction studies of the "upper plexus" type. To demonstrate slowing with the "upper type" one would have to record in the musculocutaneous or deltoid muscles.
This hypothetical statement is not the case in our clinical experience.
To understand our technique and results one must look at two observations—the anatomy of the brachial plexus and the sites of stimulation and recording. The clinical diagnosis is established by sensory symptoms in most patients. The sensory supply to the thumb is the C6 nerve root, the sensory distribution to the index and middle fingers is C7, and that for the fourth and fifth digits is from the C8 nerve root. Patients with symptoms in the C6 and C7 nerve root area were identified in our report as having the upper type of TOS [5], with compression at the level of the upper or middle trunks, or both [2]. The corroborating test is the stimulation of motor fibers of C6 and C7 in the upper and middle trunks. The pickup muscle for C6 and C7 fibers is the (opponens pollicis), which is supplied by fibers from C6 and C7 nerves [6] (Gray’s Anatomy). If there is a decrease in velocity, it substantiates pressure on these trunks. Contrarily, if symptoms are in the C8 or lower type of TOS, the corroborating test is the stimulation of the fibers at the level of the lower trunk of the brachial plexus, and the "pickup" muscle is the abductor digiti minimus. If there is decreased velocity in this study it substantiates the pressure on the lower trunk. The site of stimulation is not the ulnar or median nerves, rather, it is at the level of the trunks of the brachial plexus [7].
The arguments put forth by Wilbourn and Cherington that the motor conduction "pickup" muscles for C5 and for C6 and C7 could not be found in any muscles of the hand is refuted by review of a classic anatomy text (Gray’s Anatomy) [6].
The fact that many physicians are skeptical with regard to the TOS "disorder" may relate to each of their clinical experiences with TOS. We would invite Wilbourn and Cherington to visit our laboratory and welcome their continued dialogue.
References
Related Article
This article has been cited by other articles:
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  A. J. Wilbourn and M. Cherington The lower plexus innervates the opponens pollicis and abductor pollicis brevis. Ann. Thorac. Surg., February 1, 2000; 69(2): 664 - 665. [Full Text] [PDF]
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J. Kimura Intrinsic hand muscles are innervated by C8 and T1, not C6 and C7, roots Ann. Thorac. Surg., February 1, 2000; 69(2): 665 - 665. [Full Text] [PDF]
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M. J. Aminoff Median-innervated intrinsic hand muscles Ann. Thorac. Surg., February 1, 2000; 69(2): 666 - 666. [Full Text] [PDF]
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