Demographics

nTOS most frequently occurs in individuals between 20 and 40 years of age, and approximately 70% of affected patients are women. nTOS may arise in individuals engaged in a variety of occupational or recreational activities, most often those involving repeated use of the arm or arms in elevated positions or after a spectrum of injuries to the head, neck, or upper extremity. nTOS may also develop in patients with no apparent predisposition (i.e., no anatomic variations or history of trauma). There are no medical conditions or known inherited patterns predisposing to nTOS. High-performance athletes engaged in baseball, football, volleyball, swimming, and rowing represent a growing number of patients who will present most demonstratively with venous TOS but who can have mixed signs of nTOS.^12,13

Pain and Paresthesia

The primary symptoms of nTOS include extremity pain, dysesthesia, numbness, neck symptoms, weakness, and swelling.⁴ These symptoms usually occur throughout the affected hand or arm without any localization to a specific peripheral nerve distribution, and they often involve different areas of the entire upper extremity. Extension of symptoms from the hand to the shoulder, neck, jawline, and upper part of the back is not infrequent, and in many patients the symptoms in the neck or upper part of the back may be perceived as the most functionally disabling and most constant. Although most patients with nTOS have symptoms affecting just one upper extremity, bilateral symptoms are not uncommon; in such cases, the dominant extremity is often more symptomatic at initial evaluation, but the opposite extremity may become involved over time, perhaps as a result of compensatory overuse. The lack of distribution of symptoms into patterns referable to a single peripheral nerve and the frequent extension of symptoms to the shoulder, neck, and back allow distinction of nTOS from more reliably treatable nerve compression disorders affecting the ulnar nerve at the elbow (cubital compression syndrome), the median nerve at the wrist (carpal tunnel syndrome), or other related conditions. Different symptomatic manifestations of nTOS may be observed, depending on the brachial plexus nerve roots that are principally involved: upper plexus disorders (nerve roots C5, C6, C7) are dominated by symptoms in the distribution of the radial and musculocutaneous nerves, whereas lower plexus disorders (nerve roots C7, C8, T1) most commonly involve the median and ulnar nerves, and often these patients will point to their inner upper arm as to where the pain seems to radiate downward. In many cases, however, it is not possible to draw these distinctions because of a wider distribution of symptoms.

Positional Effects

Almost all patients affected by nTOS describe reproducible exacerbation of symptoms by activities that require elevation or sustained use of the arms or hands. These activities may include simply reaching for objects overhead, lifting, prolonged typing or work at computer consoles, driving a motor vehicle, speaking on the telephone, shaving, and combing or brushing the hair. Positional effects may also be brought on by lying supine, especially when the arms are positioned overhead, and can result in pain and difficulty sleeping at night. Documentation at baseline of activities of daily living and the inability to perform certain routine household chores, work activities, or recreational efforts is one of the more recent advances in the literature related to nTOS.^4,14 This clear documentation by QOL outcomes surveys allows surgeons to more accurately document postoperative improvement, or lack thereof, and is particularly helpful when reviewing a surgeon’s outcomes.

Weakness and Muscle Atrophy

Prolonged, severe extrinsic compression of peripheral nerves can result in muscle weakness and atrophy, but such findings occur much less than the pain and paresthesias that most patients will describe. This lack of atrophy is probably because of the intermittent nature of nerve compression in nTOS, which produces pain and other neural symptoms but prevents permanent motor nerve dysfunction. Most commonly, hand or arm pain with use of the affected extremity may lead to the perception of weakness and cause the patient to avoid use of the arm or positions that exacerbate symptoms; this distinction should be sought during evaluation to help identify other conditions that may be responsible for the symptoms of muscle weakness. Many times the athletes that present for possible nTOS have noted a dropoff in performance and report the inability to push the arm to extreme limits in endurance activities. The presence of authentic muscle weakness may therefore indicate particularly severe and long-standing compression of the brachial plexus nerve roots as a result of nTOS or another condition. Obvious atrophy is also seen when a cervical rib is present and the brachial plexus roots have been severely distorted in the scalene triangle.

Disability

The majority of individuals with positional complaints related to nTOS are affected to only a mild and tolerable degree. These symptoms are usually due to transient irritation of the brachial plexus with certain positions of the arm or during certain activities, and to some extent, such symptoms are frequent in the normal population. Little risk of progressive injury exists in these situations, and no specific intervention is warranted. Patients inquiring whether their arm discomfort or disability will lead to permanent damage can usually be reassured that with positional exercises, avoidance of certain activities, and good physical therapy, it is unlikely they will progress to severe permanent disability.

However, a smaller number of patients with clinically significant nTOS will exhibit progressively disabling symptoms that effectively prevent them from working, playing, or carrying out simple daily activities. These patients often describe progressive disability and a long history of consultations with different physicians and partial or ineffective treatments. By the time nTOS is considered, many patients have seen physical therapists, orthopedists, physiatrists, chiropractors, and spine surgeons. Such patients may have been prevented from working for a long time before consultation or may have attempted to persist in work-related activities despite ongoing neurogenic symptoms. Part of the initial assessment of a patient with nTOS is therefore concerned with assessing the extent of the patient’s disability and expectations for the potential to continue or return to work. It is particularly helpful in this regard to obtain a detailed description from the patient of activities that exacerbate the symptoms associated with nTOS, as well as activities normally required in the workplace. Documentation of this assessment is often important if restrictions from work are necessary in the management of these patients and in guiding decisions about the role of surgical treatment. One such instrument described and validated in the literature is the QuickDASH (QD) questionnaire (DASH = disability of the arm, shoulder and hand).^4,14–16 This survey for disorders of the upper extremities has been extensively validated in orthopedic and hand surgery literature; recently, it has been increasingly used in nTOS outcomes reports. The QD instrument uses 11 items to objectively measure physical function and symptoms in people with any single or multiple musculoskeletal disorders of the upper limb. Scores range from 0 points (asymptomatic) to 100 (totally incapacitated). More information is available online (http://www.dash.iwh.on.ca/).

Arterial Symptoms and Complex Regional Pain Syndrome

Vascular symptoms, especially those ischemic in nature, should be specifically sought in the history of patients with suspected nTOS, particularly discoloration or coldness in the hands and fingers. It is important to note that ischemia is actually very unusual in such patients, whereas symptoms of vasomotor disturbance are not uncommon in those with long-standing or severe nTOS. Indeed, in some patients, the symptoms of TOS may have progressed to resemble those of complex regional pain syndrome type I (CRPS-I; formerly known as reflex sympathetic dystrophy [RSD]), characterized by persistent vasospasm, disuse edema, and extreme hypersensitivity. The acuity of these symptoms often leads to avoidance and withdrawal from even light touch of the affected extremity. The diagnosis of CRPS-I can be supported by vascular laboratory studies revealing abnormal vasoconstrictive responses (cold pressor tests) or imaging studies of the hand microcirculation, but in most cases the diagnosis is made on clinical grounds. Identification of this condition in patients with nTOS is important because it may lead to an earlier recommendation for operative treatment and consideration of concomitant cervical sympathectomy.

When a history suggesting arterial insufficiency or thromboembolism exists, vascular laboratory studies and cross-sectional imaging with contrast or extremity arteriography may be necessary to exclude the presence of subclavian artery aneurysm or occlusive disease. Remember that solely relying on contrast arteriography will illustrate only the arterial lumen and could miss a subtle subclavian aneurysm or poststenotic dilatation that contains thrombus. Conversely, a history of arm swelling, cyanotic discoloration, and distended subcutaneous collaterals may indicate venous TOS secondary to obstruction of the subclavian vein, which may require venography for full evaluation. Identification of these conditions in patients with nTOS is vital because the coexistence of neurogenic and vascular forms of TOS will have an impact on the decisions and plans for surgical treatment.

The Adson maneuver is commonly used to identify positional compression of the subclavian artery by detecting ablation of the radial pulse when the patient inspires deeply and turns the neck away from the affected extremity, with or without elevation of the arm (see Chapters 125 and 127) Although this maneuver does not specifically reveal nerve root compression, positive findings may be associated with nTOS.⁴ It is important to recognize that a positive Adson sign is also common in the asymptomatic general population. This maneuver may therefore serve to support but not prove the diagnosis of nTOS. It is equally important to recognize that negative findings of arterial compression do not exclude a diagnosis of nTOS. Most physicians experienced with TOS therefore find the Adson test to be of little specific value; however, documentation of this test and its findings can aid in the explanation to the patient of abnormal findings with odd symptoms.

Patients with symptoms of nTOS may on occasion have vascular findings related to either arterial or venous TOS. It is important that these conditions be identified early in the evaluation because their presence may lead to specific tests and modified treatment recommendations. During physical examination, the surgeon should seek evidence of arterial compromise to the upper extremity, such as sympathetic overactivity with vasospasm, digital or hand ischemia, cutaneous ulceration or emboli, forearm claudication, or the pulsatile supraclavicular mass or bruit characteristic of a subclavian artery aneurysm. Comparison of blood pressure in each arm is also valuable to identify any evidence of arterial occlusion. Venous TOS, in contrast, may be associated with hand and arm edema, cyanosis, enlarged subcutaneous collateral veins, and early forearm fatigue in the absence of arterial compromise.

Radiography

Plain radiographs of the neck are helpful in determining whether an osseous cervical rib or an abnormally wide transverse process of the cervical vertebrae is present. Although each of these findings may solidify the diagnostic impression of TOS, neither of them is essential. Still, finding patients with cervical ribs who present with signs and symptoms consistent with nTOS is important, because that patient cohort often benefits significantly from operative intervention.¹⁷

Cross-Sectional Imaging

The results of computed tomography, MRI, and other imaging examinations are usually negative in nTOS because the anatomic factors leading to intermittent or positional nerve compression are generally beyond the resolution of these studies. Even in situations in which an apparent imaging abnormality exists in the region of the scalene triangle, it is usually impossible to prove the functional importance of such abnormalities with respect to the patient’s upper extremity complaints. Imaging studies are nonetheless important to exclude other conditions that could be responsible for the upper extremity symptoms, such as degenerative cervical disk or spine disease, shoulder joint pathology, or various forms of intracranial pathology.

In recent years, advances in MRI and data processing have led to higher resolution scans with three-dimensional reconstruction, along with the ability to detect localized abnormalities in nerve function (MR “neurography”).^18,19 As this technique becomes used more frequently in patients with and without nTOS, it may provide an improved diagnostic tool to supplement clinical evaluation with an accurate “objective” test for this challenging problem. There remains a need, however, for better studies to document the predictive factors of these MRIs for nTOS and whether they make a difference in the operative approach or selection of these patients. A more challenging scenario occurs when a patient presents with expectations of surgery based on high-resolution MRI results that say “positive” for compression of the brachial plexus. As will be described later, having an algorithmic approach to patient selection will help with standardizing one’s practice and likely improve patient expectations and outcomes.

Neurophysiologic Testing

Electromyography (EMG) and nerve conduction studies (NCS) are often used early in the evaluation of patients suspected of having nTOS, particularly when the symptoms are suggestive of a specific radiculopathy, a peripheral nerve syndrome, or a general myopathy. Positive results of neurophysiologic testing are therefore useful in that they point to specific conditions that must be evaluated further. Unfortunately, the results of conventional EMG/NCS are usually negative in nTOS because the nerve root compression occurs in a proximal location, is intermittent, and is not typically associated with permanent changes in motor nerve function.²⁰ Negative results from these studies are nonetheless valuable in the diagnostic evaluation of some patients by excluding other conditions from further consideration. Positive EMG/NCS findings in patients with suspected nTOS are a poor prognostic sign in the absence of an alternative explanation because they indicate an advanced stage of neural damage that may be unlikely to resolve despite adequate decompression. Recent evidence suggests that electrophysiologic testing of sensory nerve abnormalities may be more useful in the diagnosis of nTOS than conventional EMG/NCS. For example, Machanic et al compared the response with medial antebrachial cutaneous nerve and C8 nerve root stimulation in 41 patients with a clinical diagnosis of nTOS and in 19 asymptomatic controls; they reported that electrophysiologic testing had a high degree of sensitivity and specificity.²¹

Scalene Muscle Blocks

Injection of local anesthetic into the anterior scalene muscle has been popularized by the UCLA group as an adjunct to the clinical diagnosis of nTOS, particularly in predicting the potential response to surgical decompression.²² A successful scalene muscle block is indicated by relief of symptoms in the hand or arm, along with a reduction in local tenderness over the anterior scalene muscle. Injection of anesthetic to the level of the brachial plexus precludes accurate interpretation of this test because the temporary numbness and weakness in the arm will make assessment of pain relief unreliable. Although scalene muscle block is not necessary in patients with clear-cut symptoms in whom the diagnosis is not questioned, it is most useful in patients with an equivocal diagnosis of nTOS. In the most recent report from the Hopkins group, Lum and colleagues²³ found success rates in the 67% to 90% range in patients operated on for nTOS who responded to lidocaine blocks, and particular improvement when using this as a distinguishing factor in patients over 40 years old. A variation of scalene muscle block as a treatment of nTOS that showed promising early results but has not been consistently reported in the literature is the use of locally injected botulinum toxin.^24,25 However, side effects of botulinum toxin may occur early after treatment (e.g., dysphagia), the duration of beneficial effects with botulinum toxin is often limited to 3 to 6 months, and the effects of repeated treatment are diminished by the systemic immune response to the injected protein. Thus in the absence of further studies, this approach cannot yet be generally recommended.

Angiography and Vascular Laboratory Studies

Vascular laboratory studies and angiography are not usually necessary in making the diagnosis of nTOS. However, patients with clinical features that suggest an arterial component of their disorder should undergo positional noninvasive vascular laboratory studies consisting of measurement of segmental arterial pressure, waveform analysis, and duplex imaging; furthermore, contrast-enhanced arteriography may be necessary to completely exclude or prove the existence of a fixed arterial lesion. Similarly, patients in whom venous TOS is suspected should be studied by duplex ultrasound, and in those who have a negative duplex study but in whom the clinical findings remain suspicious for venous TOS, contrast-enhanced venography should be performed if not done previously in the context of an “effort thrombosis” event. In each case, it is important to specifically seek out positional maneuvers during the performance of these diagnostic tests and to consider bilateral studies if any suggestion of contralateral symptoms exists.