Thoracic outlet syndrome (TOS) is a condition in which there is compression of the nerves, arteries, or veins in the superior thoracic aperture, the passageway from the lower neck to the armpit, also known as the thoracic outlet. There are three main types: neurogenic, venous, and arterial. The neurogenic type is the most common and presents with pain, weakness, paraesthesia, and occasionally loss of muscle at the base of the thumb. The venous type results in swelling, pain, and possibly a bluish coloration of the arm. The arterial type results in pain, coldness, and pallor of the arm. TOS may result from trauma, repetitive arm movements, tumors, pregnancy, or anatomical variations such as a cervical rib. The diagnosis may be supported by nerve conduction studies and medical imaging. TOS is difficult to diagnose and there are many potential differential diagnoses as well as other diseases that are often co-occurrent with TOS. Initial treatment for the neurogenic type is with exercises to strengthen the chest muscles and improve posture. NSAIDs such as naproxen may be used for pain. Surgery is typically done for the arterial and venous types and a decompression for the neurogenic type if it does not improve with other treatments. Blood thinners may be used to treat or prevent blood clots. Due in part to inconsistent definitions and diagnostic criteria among TOS research, the true incidence of TOS is unknown; estimates have ranged from as low as a handful per 100,000 to around 1% of the population. It is more common in women than men and it occurs most commonly between 20 and 50 years of age. The condition was first described in 1818 and the current term "thoracic outlet syndrome" first used in 1956.
Signs and symptoms TOS affects mainly the upper limbs, with signs and symptoms manifesting in the shoulders, neck, arms and hands. Pain can be present on an intermittent or permanent basis. It can be sharp/stabbing, burning, or aching. TOS can involve only part of the hand (as in the pinky and adjacent half of the ring finger), all of the hand, or the inner aspect of the forearm and upper arm. Pain can also be in the side of the neck, the pectoral area below the clavicle, the armpit/axillary area, and the upper back (i.e., the trapezius and rhomboid area). Discoloration of the hands, one hand colder than the other hand, weakness of the hand and arm muscles, and tingling are commonly present. Only 1% of people with carpal tunnel syndrome have concomitant TOS. Repetitive motions can cause enlargement of muscles which causes compression of veins. Besides, overuse injury of the upper limbs causes swellings, small bleeding, and subsequent fibrosis which would cause the thrombosis of the subclavian vein, leading to Paget–Schroetter disease or effort-induced thrombosis. Pemberton's sign is a clinical sign elicited by having the patient hold their arms above their head for 1 minute. The development of facial plethora, cyanosis, inspiratory stridor and non-pulsatile elevation of the JVP is indicative of TOS. TOS can be related to cerebrovascular arterial insufficiency when affecting the subclavian artery. It also can affect the vertebral artery, in which case it could produce vision disturbances, including transient blindness, and embolic cerebral infarction. TOS can also lead to eye problems and vision loss as a circumstance of vertebral artery compression. Although very rare, if compression of the brain stem is also involved in an individual presentation of TOS, transient blindness may occur while the head is held in certain positions. If left untreated, TOS can lead to neurological deficits as a result of the hypoperfusion and hypometabolism of certain areas of the brain and cerebellum. TOS has similar symptoms to pectoralis minor syndrome (PMS), which usually results from compression of the brachial plexus beneath the pectoralis minor muscle (while neurogenic TOS is caused by compression of the same nerves above the clavicle). Unlike TOS there are typically few headaches or neck pain in patients with PMS only, instead there is pain in the chest area. Initially, it was believed that 95 percent of patients with TOS had nerve compression in the scalene area, but in the twenty-first century it is now recognized that the majority have nerve compression under the pectoralis minor, either by itself or in addition to the scalene area. One study of 100 patients diagnosed with neurogenic TOS found that 75 percent had neurogenic PMS and 30 percent in fact had PMS without TOS.
Causes
TOS can be attributed to one or more of the following factors:
Congenital abnormalities are frequently found in persons with TOS. Bone abnormalities include the presence of a cervical rib and a prolonged transverse process. Soft tissue abnormalities include scalene muscle hypertrophy, the presence of a fourth scalene muscle (scalenus minimus), or connective tissue abnormalities. Trauma (e.g., whiplash injuries) or repetitive strain is frequently implicated. Injury, such as first rib fracture or clavicle fracture. Rarer acquired causes include tumors (especially pancoast tumor), hyperostosis, and osteomyelitis. Up to 15% of neurogenic TOS cases are idiopathic.
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