There are several possible causes of left shoulder and left arm pain: first, cervical spondylosis, when there is cervical spondylosis, there can be symptoms of left shoulder and left arm pain, then you should have relevant cervical spine X-ray and CT, nuclear magnetic examination for early diagnosis and treatment; second, myofasciitis, patients with myofasciitis often have pain on the inner side of the scapula as the first symptom, which can radiate to the ipsilateral shoulder and arm. In myofasciitis, the first symptom is pain in the medial side of the scapula, which can be radiated to the ipsilateral shoulder and arm, with vague or radiating pain.