Thoracic outlet syndrome (TOS) is a condition caused by compression of the nerves, arteries, or veins in the space between the collarbone and first rib. It can lead to symptoms such as pain, numbness, tingling, weakness, or reduced circulation in the neck, shoulder, arm, or hand. Diagnosis typically involves a physical examination, medical history, and imaging or nerve function tests. Treatment depends on the underlying cause and severity of symptoms and may include physical therapy, medications, minimally invasive procedures, or surgery. Early evaluation and appropriate management can help relieve symptoms and improve function and circulation.