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Confounding Aspects
There are also four confounding aspects of TOS that need explanation and understanding. Not all of these features will necessarily be represented in all patients.
Regional Myofascial Pain
First, as on pp 201 of my 1991 article (Appendix 2), you will see references to muscle spasms in the region of the thoracic outlet. The commonest muscles involved in this process are the scalene muscles, pectoralis minor, trapezius, levator scapulae, and the para cervical muscles posteriorly. We often refer to this as a regional myo-fascial pain syndrome. How it relates to TOS remains unclear, but myo-fascial pain becomes a significant part of the whole when assessing patients with TOS.
Sympathetically Mediated Pain
Second, as on pp 203 of my 1991 article, you will see references to autonomic or sympathetically mediated symptoms. Postganglionic sympathetic fibres join the C8 and T1 peripheral nerve roots in the precise area of the thoracic outlet compression.
Sympathetically mediated pain, alternatively called causalgia, reflex sympathetic dystrophy or regional pain syndrome is the other confounding circumstance. This condition exists as a 'stand-alone' condition in less than 1 in 1000 otherwise normal people. However, degrees of sympathetic dysfunction are seen in as many as 30% of patients with symptomatic TOS.
Upper vs Lower Root TOS
Third, how can one explain the notion that thoracic outlet syndrome can cause sensory symptoms in both the ulnar and/or the median aspects of the hand? 'It's not anatomical to have sensory symptoms involving all of the fingers and the thumb', the inexperienced observer is often heard to say.
Much talk has been generated in the literature regarding upper plexus (trunk, cord, root) TOS, lower plexus TOS or mixed TOS. I refer the reader to the brachial plexus diagrams above.
The two main peripheral nerves that appear at the wrist level are the median and the ulnar nerves. The ulnar nerve is made up of motor and sensory fibres that come from spinal roots of C8 and T1. The median nerve is made up of fibres that come from spinal roots of C5, 6, 7, 8 andT1. Whilst the median nerve carries fibres from the entire brachial plexus, the sensory fibres come only from C5, 6, and 7.
The five nerve roots, C5-8 and T1 become the brachial plexus amalgamating to form three cords. The middle or posterior cord innervates the shoulder, the upper arm and the wrist extensors. The upper cord becomes the supplier of C5, 6 fibres to the median nerve, whilst the lower cord supplies the C8-T1 fibres to the ulnar nerve. Therefore, from the anatomical perspective, the upper plexus becomes (for the most part) the median nerve, and the lower plexus becomes the ulnar nerve. This is important because of the clinical observations that follow.
For decades, observers have been puzzled to note that some cases of TOS present with radial-side hand symptoms seem to emulate carpal tunnel syndrome; C 5-6 (median nerve entrapment at the wrist), whilst the majority of TOS cases seem to involve the nerve distribution of the ulnar nerve; C8-T1, sometimes emulating ulnar nerve entrapment at the elbow. As long ago as 1944 Swank and Simeone (reference 125 in my 1991 article) postulated the notion of upper and lower plexus (trunk, root, cord) TOS.
These pioneering observations have now lead to the modern practice of thinking of symptomatic TOS as being consistent with upper plexus, lower plexus or both upper and lower mixed compression.
A publication by Urschel HC and Razzuk MA details a lengthy and prolific experience with the surgical treatment of TOS (Ann Surg 1998 Oct; 228 (4): 609-617). This is the largest published experience with the surgical management of thoracic outlet syndrome. Of 2210 patients, 250 had symptoms of upper plexus compression (11.31%), 1508 (68.24%) had lower plexus involvement and the remaining 452 (20.45%) were described as having mixed upper and lower plexus TOS.
All of this implies that it is possible to have symptoms of paresthesiae involving the entire hand on the basis of compression of the brachial plexus by congenital anomalies at the level of the thoracic outlet.
Double Crush Syndrome
The fourth confounding aspect of TOS speaks to the concurrent findings of both symptomatic thoracic outlet syndrome and carpal tunnel syndrome in the same patient. I draw the reader's attention to p.201 of my 1991 article (Appendix2). It is not uncommon to find thoracic outlet syndrome and carpal tunnel syndrome co-existing in the same patient, an example of the so-called 'double crush' syndrome. Simply stated, 'double crush' means that if any given nerve is subjected to a proximal compressive neuropathy then it is more prone to the development of a second or 'double' distal neuropathy. If the patient is significantly disabled by these conditions, we tend to decompress the carpal tunnel as an initial step since that surgery is of lesser morbidity than first rib resection. Many patients will manage without coming to surgery for their TOS.
For patients coming to surgery, the following informed consent advice is always provided. All surgeries carry some risk. It is reported that <0.1% of patients coming to first rib resection may suffer intra-operative injury of the great vessels or the brachial plexus. Twenty percent of patients do not improve following transaxillary first rib resection, but the remaining 80 percent will be the partially or completely symptom-free two years following operation. Fifty of the 80 will be completely symptom free, whilst 30 will be improved but carry some ongoing symptoms.
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