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Ann Thorac Surg 1999;67:290-291
© 1999 The Society of Thoracic Surgeons

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Correspondence

Diagnosing upper plexus thoracic outlet syndrome with median motor nerve conduction studies

^a The Cleveland Clinic Foundation, 9500 Euclid Ave, Cleveland, OH 44195, USA
^b Centura Health, St. Anthony Hospital, 4231 West 16th Ave, Denver, CO 80204, USA

To the Editor

We are writing regarding an article, authored by Urschel and Razzuk [1], that appeared in The Annals last year. They recommended performing a median motor nerve conduction study (NCS) using supraclavicular stimulation to diagnose the upper plexus type of thoracic outlet syndrome (TOS). They reported finding slowing across the thoracic outlet with that procedure. However, the upper plexus customarily is defined as the C5, C6 roots and upper trunk; the authors added the C7 root which, along with the middle trunk, usually is designated the middle plexus. Regardless, none of the median motor axons that innervate intrinsic hand muscles (which serve as the recorded muscles during the median motor NCS) traverses any of these structures. Instead, they all derive from the C8, T1 roots/lower trunk (ie, lower plexus) and thus travel the same plexus pathway as the ulnar motor axons that supply intrinsic hand muscles. In contrast, the median axons that traverse the upper and middle plexus provide sensation to the median-supplied fingers, and innervate various forearm muscles, eg, pronator teres [2]. Given the anatomy, it is illogical to expect an upper plexus lesion to cause slowing along nerve fibers assessed with a median motor NCS. If motor conduction slowing across the thoracic outlet occurs with TOS—and most experienced electromyographers deny that it does—then it should be found by both median and ulnar motor NCS with lower plexus TOS, and should be undetected by either NCS with upper plexus TOS. To demonstrate slowing with the latter would require recording from muscles innervated by the upper plexus (eg, musculocutaneous, deltoid) while supraclavicularly stimulating the nerves supplying them [2].

Both clinicians and electromyographers must be familiar with brachial plexus anatomy, if lesions affecting that structure are to be localized correctly. In addition, if a proposed electrodiagnostic procedure is to be valid, it must withstand the scrutiny of independent investigators and have its use confirmed in other electromyographic laboratories. Unfortunately, many patients are diagnosed as having neurogenic TOS based on tests that subsequently are refuted. The authors previously advocated a similar electrodiagnostic method for identifying lower plexus TOS, using the ulnar motor NCS [3]. That procedure, challenged by independent examiners, became the subject of an editorial in the New England Journal of Medicine [4]. We encourage readers to review the comments in that editorial.

In summary, it appears that Urschel and Razzuk’s recognition of upper plexus TOS and their reported high success rate of treating it with transaxillary first rib resection were based on electrodiagnostic data (ie, on NCS changes) that could only be found with lower plexus TOS. This inconsistency exemplifies one of the reasons why so many physicians are skeptical regarding this disorder and its surgical treatment.

References

1. Urschel H.C., Jr, Razzuk M.A. Upper plexus thoracic outlet syndrome: optimal therapy. Ann Thorac Surg 1997;63:935-939.[Abstract/Free Full Text]
2. Wilbourn A.J. Assessment of the brachial plexus and the phrenic nerve. In: Johnson E.W., Pease W.A., eds. Practical electromyography, 3rd ed. Baltimore, Maryland: Williams & Wilkins, 1997:273-310.
3. Urschel H.C., Razzuk M.A. Management of the thoracic outlet syndrome. N Engl J Med 1972;286:1140-1143.
4. Relman A.S. Responsibilities of authorship: where does the buck stop?. N Engl J Med 1984;310:1048-1049.[Medline]

This article has been cited by other articles:

				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]

				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]

				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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