Question category: Neurology
A 22 year old male presents with left shoulder pain which is severe and stabbing in nature. He also notices some weakness when lifting things high. On examination there is muscle wasting at the shoulder and 4/5 power in the extensors. There is absence of the biceps and supinator reflexes. There is reduction in sensation in the lateral aspect of the arm. There is nil else of note on examination. Which of the following in the most likely diagnosis?