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. The presence of these findings indicates irritation of the large nerve trunks above the collarbone (brachial plexus), which is diagnostic for TOS. If, in addition, there is either a constant pallor to the hand (which has turned white and possibly has multiple red spots) or gross swelling throughout the hand and arm with a dusty-bluish/purplish tinge, the problem points to a serious disorder of the artery or vein, requiring rapid surgical intervention by a vascular surgeon. The vast majority of cases (95+%) do not show these extreme findings but do show some mild swelling or discoloration, which should not be confused with frank arterial or venous pathology. One should also bear in mind that other disorders can cause generally similar symptoms and include pathologies at the neck, shoulder, and shoulder blade, as well as the very rare tumor. A variety of systemic diseases can produce these symptoms through other mechanisms that irritate the brachial plexus. Because of this, a thorough blood and imaging workup is a routine requirement and includes analyses for systemic diseases (autoimmune, hormonal, and tumorous), x-ray for both bony and spinal abnormalities, and electrodiagnostics for frank peripheral neuropathies. Magnetic resonance imaging...