Thoracic outlet syndrome (TOS) is a condition that occurs when blood vessels or nerves in the upper chest are compressed. This can lead to pain, numbness, and weakness in the shoulders, arms, and hands. TOS can result from various factors, including anatomical abnormalities, injuries, or repetitive activities that strain the area. There are three main types of TOS: neurogenic, which affects the nerves; venous, which affects the veins; and arterial, which affects the arteries. Diagnosis typically involves a physical examination and imaging tests. Treatment options may include physical therapy, medication, or, in severe cases, surgery.