There are several possible causes of pain in the left arm: first, shoulder diseases, when the shoulder has frozen shoulder or rotator cuff tears, rotator cuff impingement syndrome, there can be pain in the upper side of the arm, at this time, we need to carry out X-ray and nuclear magnetic examination of the shoulder joint for early diagnosis and treatment; second, cervical spondylosis, cervical spondylosis can compress the nerve roots and cause pain in the arm. In this case, X-ray, CT and MRI of the lumbar spine should be performed for early diagnosis and treatment; thirdly, myofasciitis, patients with myofasciitis can have pain in one shoulder and arm radiologically, which can be accompanied by symptoms of soreness and weakness, so relevant investigations and examinations should be performed to exclude other diseases for early diagnosis and treatment; fourthly, dermatomal neuritis, if the local dermatomal Fourth, dermatomal neuritis, if the local skin nerve above the arm is stuck, chronic inflammation can occur, the pain above the arm, then the relevant examination should be carried out to diagnose and treat.