Adson's sign is often an indicator of thoracic outlet syndrome. It is the decrease in ipsilateral radial pulse and/or the presence of subclavian bruit when the patient extends the neck maximally, rotating head towards the side being tested, and holding his/her breath.
These symptoms are due to compression of the brachial plexus and subclavian vasculature, and will manifest in complaints ranging from diffuse arm pain to a sensation of arm fatigue, often aggravated by carrying anything in the ipsilateral hand or doing any overhead work such as arranging objects in an overhead shelf.
The test is performed by having the patient in a sitting position, hands resting on thighs. The doctor then palpates both radial pulses as the patient rapidly fills the lungs by deep inspiration and, with breath held, hyperextends the neck and turns the head toward the 'affected' side. If the radial pulse on that side is decidedly or completely absent, the result is considered positive