Snapshot A 25-year-old woman with no history of trauma presents with right arm pain. She reports that her right arm is easily fatigable, especially after she cooks. She is a chef and denies any history of smoking, hyperlipidemia, or peripheral artery disease. On physical exam, her right upper extremity is pale and cool to the touch. Her distal right radial pulse is diminished compared to her left. Radiography reveals a cervical rib. Introduction Clinical definition syndrome resulting from compression/obstruction of the lower trunk of the brachial plexus and subclavian vessels as it passes through the thoracic outlet the thoracic outlet is above the first rib and behind the clavicle classified into three types neurogenic (compression of brachial plexus) arterial (obstruction in arteries) venous (obstruction in veins) Epidemiology demographics adults Etiology bony cervical rib an extra rib arising from 7th cervical vertebra rudimentary first rib soft tissue fibrous band from the first rib to the tip of C7 transverse process hypertrophy of nearby muscles (e.g., sternocleidomastoid or scalene muscle) more commonly in weightlifters or athletes Pancoast tumor causing compression cysts trauma Pathogenesis compression of brachial plexus can cause neuropathies compression of subclavian vein or artery can cause pain and edema Presentation Symptoms neurogenic difficulty grasping or gripping numbness and tingling in ulnar distribution pain or weakness with elevation or repetitive use of the affected arm arterial claudication diffuse arm and hand pain fatigue and ache, especially after exertion of muscle venous upper extremity swelling diffuse arm or hand pain Physical exam careful neurovascular exam should be performed neurogenic atrophy of intrinsic hand muscles decreased sensation in ulnar nerve distribution reproducible pain with elevation of arms arterial pallor and cool upper extremities weak or absent radial or ulnar pulse may have decreased blood pressure in the affected arm venous edema cyanosis of upper extremity distended veins Imaging Radiographs indication may reveal bony abnormalities findings cervical or rudimentary first rib Pancoast tumor Magnetic resonance imaging (MRI) indication may reveal soft tissue abnormalities Ultrasound indication if vascular TOS is suspected finding vascular compression Angiography indication if vascular TOS is suspected but ultrasound is unrevealing or further clarification is needed finding compression Studies Making the diagnosis most cases are clinically diagnosed Differential Other causes of vascular compromise, such as emboli distinguishing factor pain worsened with exertion of the affected muscle and relieved with rest Treatment Conservative physical therapy indication for all patients Medical nonsteroidal anti-inflammatory drugs (NSAIDs) indication pain management anticoagulation indication patients with suspected thrombosis causing compression Operative surgical decompression indications patients with fibrous band patients with cervical rib pain refractory to conservative management Complications Aneurysm formation (post-stenotic) Thromboembolism