Diagnosis
A careful history and physical examination are critical for accurate diagnosis. The diagnosis of TOS includes history, physical and neurological examinations, films of the chest and cervical spine, electromyogram, and nerve conduction velocity tests (NCV).
The multiple physical signs of thoracic outlet compression and the classic diagnostic tests will need to be thoroughly reviewed. Other causes of TOS-like symptoms, such as cardiac or pulmonary disease, must be ruled out. The electromyogram should be normal, eliminating other neuromuscular disorders. In some cases with atypical manifestations, other diagnostic procedures such as cervical myelography, peripheral or coronary arteriography, or phlebography should be considered. A detailed history and physical and neurologic examinations can often 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 NCV.
The primary objective test for thoracic outlet peripheral nerve compression in our clinic is the nerve conduction velocity (NCV). This test was improved and popularized at Baylor University Medical Center by Krusen, Caldwell and Crane. Reduction in NCV to less than 85 m/s of either the ulnar or median nerves across the thoracic outlet corroborates the clinical diagnosis.
Clinical Maneuvers
The clinical evaluation (during the physical examination) 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:
Adson or Scalene Test
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.
Costoclavicular Test (military position)
The shoulders are drawn downward and backward. 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.
Hyperabduction Test
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.
Roos Test
Both arms are placed at right angles to the shoulder and the forearms are at right angles to the upper arms. Both hands are opened and closed as fast as possible to see if symptoms occur.
Nerve Conduction Velocity (NCV)
Motor conduction velocities of the ulnar, median, radial, and musculocutaneous nerves can be reliably measured, as described by Jebson. Caldwell and Associates improved and adapted to clinical use the technique of measuring NCV in evaluating patients with thoracic outlet compression. Conduction velocities over proximal and distal segment of the ulnar and median nerves are determined by recording the action potentials generated in the hypothenar or first dorsal interosseous muscles. The points of stimulation are the supraclavicular fossa, mid-upper arm, area below the elbow, and wrist. The Meditron 201-AD or the TECA B-3 electromyogram including the coaxial cable with three needle or surface electrodes can be used for this examination. The normal NCV values are 85 m/s across the thoracic outlet, 55 m/s around the elbow, 59 m/s in the forearm, and 2.5 to 3.5 m/s at the wrist. In patients with thoracic outlet syndrome, the average NCV value is reduced to 53 m/s across the outlet (range of 32-65 m/s), as reported by Urschel and Colleagues.