Will the True Neurogenic Thoracic Outlet Syndrome Please Stand Up?
abstract & commentary
Source: Le Forestier N, et al. True neurogenic thoracic outlet syndrome: Electrophysiological diagnosis in six cases. Muscle Nerve 1998;21:1129-1134.
Six women, ages 21-63 years, with unilateral hand wasting (symptom duration 3-72 months), were found on radiography to have bilateral accessory cervical ribs (n = 3) or bilateral elongated C7 transverse processes (n = 3). Pain was the initial symptom in five, and localized to the medial arm, forearm, hand, or entire limb, with only slight and intermittent paresthesiae. One patient had three years of hand weakness only, but none had symptoms of vascular compromise. Significant thenar, and less so hypothenar, atrophy was evident on examination, with only slight (n = 3) or no (n = 3) sensory loss, involving the fifth digit/C8 territory. Long, finger flexor deep, tendon reflexes were diminished in only two, but all expressed pain on lateral neck pressure. Motor nerve conduction studies demonstrated absent or decreased median, and less so, ulnar amplitudes without conduction block or slowing on Erb’s point stimulation, and F-wave abnormalities mirrored the decreased motor amplitudes. Sensory nerve conduction studies demonstrated normal median and radial nerve amplitudes, reduced (n = 3) or absent (n = 1) ulnar responses, and reduced (n = 1) or absent (n = 5) medial antebrachial cutaneous nerve responses. Needle EMG was limited to intrinsic hand muscles and revealed chronic changes only. Surgery confirmed stretching of the lower trunk of the brachial plexus over a fibrous band in all six and, following removal of the fibrous elements, without rib resection, relief of pain was appreciated within four weeks, without improvement of weakness or electrodiagnostic findings (at 1 year). Neurogenic thoracic outlet syndrome is a rare but true condition with specific electrodiagnostic findings, particularly an absent or reduced medial antebrachial cutaneous nerve response, and in the presence of bony structural radiographic abnormalities warrants surgical intervention.
Commentary
The thoracic outlet (or "inlet," depending on perspective) is a crowded area at the apex of the lung, above the first rib and below the clavicle, which allows passage of the subclavian artery, vein, and brachial plexus into (and out of) the arm. Thoracic outlet syndrome (TOS), a general term implying compression of one or another of these structures, may, thus, be more precisely characterized as 1) arterial TOS (compressing the subclavian artery, resulting in arm, hand, and finger pallor and ischemia); 2) venous TOS (compressing the subclavian vein, resulting in arm swelling and edema); or 3) neurogenic TOS (compressing the lower trunk/medial cord of the brachial plexus and resulting in the condition described above). All are rare but true and accepted forms of TOS that, in the presence of the appropriate clinical picture, would be agreed upon by a consensus of qualified physicians. Clinical confusion and controversy arises, however, when the many patients with chronic, nonspecific, arm pain and paresthesiae are inappropriately labeled TOS in the absence of objective neurologic, electrophysiologic, or vascular abnormalities. Most of these patients do not have true TOS and may be termed "disputed neurologic TOS" (Wilbourn AJ. Muscle Nerve 1988;11:66-74). It is this condition that results in unusual surgical patterns, including 174 patients in Colorado who underwent surgery for TOS in 1989 alone (a veritable epidemic!)—almost all of whom had private insurance or worker’s compensation. Curiously, Medicaid patients almost never underwent surgery (Cherington M, Cherington C. Neurology 1992;42:943-945). Unless strict criteria are adhered to, surgeons will continue to operate unnecessarily, and although highly successful in up to 90%, conservative management is equally so without the attendant risks, which, when measured against the benefits, are unacceptably high (Porter JM, et al. Vasc Diagn Ther 1982;3:35-42; Wilbourn AJ. Ibid).
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