Pain in the left arm for unknown reasons is most often neuropathic. The neuropathic pain in the left arm may be caused by the following two factors: 1. It may be caused by frozen shoulder on the left side, where inflammation around the left shoulder joint affects the anterolateral cutaneous nerve of the left upper arm, resulting in pulling pain in the anterior or lateral cutaneous nerve of the left upper arm. This condition is usually accompanied by pain in the shoulder joint with limited movement in addition to pain in the left arm.2. It may be caused by cervical spondylosis, a degenerative change in the cervical spine, such as osteophytes, herniated discs or small joint misalignment compressing the nerve roots on the left side, resulting in nerve pulling pain in the left upper limb, accompanied by numbness and other symptoms. However, in addition to unexplained pain in the left arm, there is also discomfort in the neck or neck and shoulder, which may induce pain in the left upper arm when the neck is moved.