The diagnosis of TOS includes history, physical and neurologic examinations, films of the chest and cervical spine, electromyogram, and ulnar nerve conduction velocity (UNCV). In some patients with atypical manifestations, other diagnostic procedures, such as cervical myelography, peripheral or coronary arteriography, and phlebography should be considered. A detailed history and physical examination, together with neurologic examination, often can result in a tentative diagnosis of neurovascular compression. This diagnosis is strengthened when one or more of the classic clinical maneuvers is positive and is confirmed by the finding of decreased UNCV.7
The clinical evaluation is best based on the physical findings of loss or decrease of radial pulses and reproduction of symptoms that can be elicited by the three classic maneuvers.
This maneuver tightens the anterior and middle scalene muscles and thus decreases the interspace and magnifies any preexisting compression of the subclavian artery and brachial plexus. The patient is instructed to take and hold a deep breath, extend the neck fully, and turn the head toward the side. Obliteration or decrease of the radial pulse suggests compression.5,10
Costoclavicular Test (Military Position)
This maneuver narrows the costoclavicular space by approximating the clavicle to the first rib and thus tends to compress the neurovascular bundle. Changes in the radial pulse with production of symptoms indicate compression. The shoulders are drawn downward and backward.5,10
When the arm is hyperabducted to 180 degrees, the components of the neurovascular bundle are pulled around the pectoralis minor tendon, the coracoid process, and the head of the humerus. If the radial pulse is decreased, compression should be suspected. 5,10
Films of the chest and cervical spine are helpful in revealing bony abnormalities, particularly cervical ribs and bony degenerative changes. If osteophytic changes and intervertebral disk space narrowing are present on plain cervical films, a cervical CT scan should be performed to rule out bony encroachment and narrowing of the spinal canal and the intervertebral foramina.
Nerve Conduction Velocity and Electromyography
This test is used widely in the differential diagnosis of the causes of arm pain, tingling, and numbness with or without motor weakness of the hand. Such symptoms may result from compression at various sites: in the spine; at the thoracic outlet; around the elbow, where it causes tardy ulnar nerve palsy; or on the flexor aspects of the wrist, where it produces carpal tunnel syndrome. For diagnosis and localization of the site of compression, cathodal stimulation is applied at various points along the course of the nerve. Motor conduction velocities of the ulnar, median, radial, and musculocutaneous nerves can be measured reliably. Caldwell and colleagues have improved the technique of measuring UNCV for evaluation of patients with thoracic outlet compression.11 Conduction velocities over proximal and distal segments of the ulnar nerve are determined by recording the action potentials generated in the hypothenar or first dorsal interosseous muscles. The points of stimulation are the supraclavicular fossa, middle upper arm, below the elbow, and at the wrist.7
Electromyographic examination of each upper extremity and determination of the conduction velocities are done with the Meditron 201 AD or 312 or the TECA-3 electromyograph; coaxial cable with three needles or surface electrodes is used to record muscle potentials, which appear on the fluorescent screen.
The conduction velocity is determined by the Krusen-Caldwell technique.12 The patient is placed on the examination table with the arm fully extended at the elbow and in about 20 degrees of abduction at the shoulder to facilitate stimulation over the course of the ulnar nerve. The ulnar nerve is stimulated at the four points by a special stimulation unit that imparts an electrical stimulus with strength of 350 V with the patient's load, which is approximately equal to 300 V, with a skin resistance of 5000 Ω. Supramaximal stimulation is used at all points to obtain maximal response. The duration of the stimulation is 0.2 ms, except for muscular individuals, for whom it is 0.5 ms. Time of stimulation, conduction delay, and muscle response appear on the TECA screen; time markers occur each millisecond on the sweep. The latency period to stimulation from the four points of stimulation to the recording electrode is obtained from the TECA digital recorder or calculated from the tracing on the screen.
The normal values of the UNCVs according to the Krusen-Caldwell technique11 are 72 m/s or above across the outlet, 55 m/s or above around the elbow, and 59 m/s or above in the forearm. Wrist delay is 2.5–3.5 ms. Decreased velocity in a segment or increased delay at the wrist indicates either compression, injury, neuropathy, or neurologic disorders. Decreased velocity across the outlet is consistent with TOS. Decreased velocity around the elbow signifies ulnar nerve entrapment or neuropathy. Increased delay at the wrist is encountered in carpal tunnel syndrome.
The clinical picture of TOS correlates fairly well with the conduction velocity across the outlet. Any value less than 70 m/s indicates neurovascular compression. The severity is graded according to the decrease in velocity across the thoracic outlet: Compression is considered slight when the velocity is 66–69 m/s, mild when the velocity is 60–65 m/s, moderate when the velocity is 55–59 m/s, and severe when the velocity is 54 m/s and below.
Simple clinical observations usually suffice to determine the degree of vascular impairment in the upper extremity. Peripheral angiography8,13 is indicated in some patients, as in the presence of a paraclavicular pulsating mass, the absence of a radial pulse, or the presence of supraclavicular or infraclavicular bruits. Retrograde or antegrade arteriograms of the subclavian and brachial arteries to demonstrate or localize the pathology should be obtained. In cases of venous stenosis or obstruction, as in Paget-Schroetter syndrome (see Chap. 125), phlebograms are used to determine the extent of thrombosis and the status of the collateral circulation.