Thoracic outlet syndrome (TOS) is a complex neurovascular compressive syndrome involving the brachial plexus, arterial, and venous structures coursing under the clavicle. Compression to the components of the brachial plexus accounts for greater than 90 percent of the cases with a frequent presentation of nighttime symptoms. These often include numbness and pain into the ulnar aspect of the arm, small and ring fingers, due to entrapment of the C8 and T1 nerves. Abduction of the arm, a common sleeping position, often initiates these symptoms which can be severe enough to awaken the patient. Other symptoms can include shoulder pain, neck pain and grip strength weakness.
The etiology, although not always identified, is variable. Congenital or developmental abnormalities include scapular abnormalities, drooping shoulders, cervical ribs, and stenosis within the neurovascular compartments formed by the attachments of the anterior and middle scalene muscle attachments to the first rib. Trauma and repetitive activities involving the shoulder girdle and brachial plexus are also felt to be contributors.
On physical examination, the presence of TOS can be associated with decrease of the radial pulse with abduction of the arm: Adson’s test when performed with the patient’s head rotated toward the tested side or Allen’s test when head rotation is to the opposite side. Unfortunately, this test is positive in a high number of asymptomatic patients. The Elevated Arm Stress Test (EAST) may be a better screen. This is performed in the sitting position with the arms abducted and the elbows flexed to 90 degrees while opening and closing the hand repetitively for three minutes. Patients with TOS will usually become symptomatic in less than three minutes. A positive EAST in the presence of a radial pulse has a higher correlation of brachial plexus compression. Grip strength weakness and atrophy of the abductor pollicis brevis may also be found. Additional work up might include radiological and MRI evaluations of the neck, brachial plexus and shoulder girdle and EMG /NCS performed above and below the clavicle.
Treatment often only requires modification of sleeping positions, body mechanics with lifting, and overhead activities. Physical therapy can be of value with stretching and strengthening exercises. In severe cases, surgical removal of the first rib or release of the anterior and middle scalene muscle attachments may prove beneficial.