Neurogenic Thoracic Outlet Syndrome

After covering vascular thoracic outlet syndrome a few weeks ago, we will move on to cover neurogenic thoracic outlet syndrome. There are some similarities and differences among these conditions, but both require a high index of suspicion. Neurogenic thoracic outlet syndrome, sometimes called nTOS, account for up to 95 percent of cases of TOS (1). It is the second most discussed nerve compression entrapment syndrome following carpal tunnel syndrome (2). This is a clinical diagnosis that describes symptomatic manifestation of compression of the brachial plexus as it traverses through the thoracic outlet. It continues to remain somewhat controversial due to it being largely subjective in nature. There have been recent developments in diagnostic studies that have allowed for more clearly-defined guidelines (1).

The brachial plexus trunks or cords, which originate from nerve roots C5 to T1, are the areas that are compressed during TOS. The areas of compression are the same as vascular TOS covered previously. Neurogenic TOS affects around 1-2 % of the population, is more common in women (about 3:1 ratio) and tends to be unilateral (1). The age range most affected is 20-60, although cases have been reported in children at age 10 (3). The lower brachial plexus is affected in about 80 percent of patients. Some will divide neurogenic TOS into true and disputed nTOS with the “true” TOS with nerve conduction slowing or needle electromyography changes.

Etiologies are similar in all variations of thoracic outlet syndrome as well. Anatomical abnormalities such as cervical or rudimentary first ribs have been shown to be more common in patients that suffer with symptoms of TOS (29 percent vs 1.1 percent) (4). Another review stated up to 20% of cases of nTOS are caused solely by a cervical first rib (5). Supernumerary scalene muscles, variant subclavius muscles and prolonged transverse processes can also cause neurogenic TOS. Fibrous bands or fibromuscular abnormalities are either congenital or acquired and are the most common cause of symptoms. Repetitive actions during labor or athletic activities make individuals more prone to nTOS symptoms. Trauma such as high impact accidents or callus from clavicle fractures can cause compression along the thoracic outlet. Malignancy, such as Pancoast tumors or osteochondromas, may also cause compression is another well-documented etiology of TOS.

Symptoms of neurogenic TOS correspond to the level of nerve compression. A systematic review by Sanders et al. described the following symptom distribution: upper extremity paresthesia (98%), neck pain (88%), trapezius pain (92%), shoulder and/or arm pain (88%), supraclavicular pain (76%), chest pain (72%), occipital headache (76%), and paresthesias in all five fingers (58%), the fourth and fifth fingers only (26%), or the first, second, and third fingers (6). Compression of the C5-7 nerves is most often distributed in the lateral neck with radiation towards the ear and occiput. The lower plexus corresponds with the C8-T1 nerves with pain distributed along the posterior shoulder with radiation down the arm in a medio-brachial distribution with paresthesias affecting mainly the ring and little fingers. Even with these typical distributions, it is still difficult to differentiate clinically (6).

Recent proposals have been made in regards to diagnostic criteria during the Consortium for Outcomes Research and Education of Thoracic Outlet Syndrome. This is a group of physicians and scientists from multiple disciplines to accurately identify and employ management strategies (7). The findings must be present for a minimum of three months and cannot be attributable to any other neurologic cause (Table 1). The Society for Vascular Surgery published reporting standards for TOS with the purpose of a clear and consistent understanding and definition nTOS. This more simplistic definition consists of the following four criteria: signs and symptoms of pathology occurring at the thoracic outlet (pain and/or tenderness), signs and symptoms of nerve compression (distal neurologic changes, often worse with arms overhead or dangling), absence of other pathology potentially explaining the symptoms and a positive response to a properly-performed scalene muscle test injection (8). The subjective nature of diagnostic finding and complaints contributes to the controversy surrounding the diagnosis.