Question category: Rheumatology
A 34 year old male presents with left neck and shoulder pain. He also notices a tingling sensation in his left forearm which is particularly noticeable on carrying his briefcase or shopping bags. He also complains of his left hand turning cold and white on occasion. On examination there is evidence of wasting in his thenar muscle and sensory loss over the ulnar aspect of the forearm. There is pallor of his left arm when elevated and loss of his left radial pulse on abduction and external rotation of his left shoulder. Which of the following is the most likely diagnosis?