The most common cause of a bump between the neck and the shoulder is inflammation and edema of the trapezius muscle, which can be caused by two factors. The first condition may be caused by long-term head-down work, life or often reading books or cell phones, which leads to muscle strain on the trapezius muscle, and over time, local aseptic inflammation will slowly appear, stimulating the local trapezius muscle to appear to have swelling, pressure pain and other symptoms. The second condition may be cervical spondylosis causing degenerative changes in the cervical spine compressing the nerve roots on the left side, which may cause pulling pain in the nerves on the left side of the neck and back of the shoulder, thus the painful stimulation may also affect the inflammation of the trapezius muscle with edema, which may cause the symptoms of bulging and pain in this area.