Patients with numbness in the left shoulder should be alert to the following diseases: First, cervical spondylosis: when cervical spondylosis protrudes the intervertebral disc or proliferates the bone to compress the nerve, it can lead to numbness in the left shoulder, then in the early stage to check the body, check the cervical MRI to make early diagnosis and early treatment. Second, tumor: nerve tumor or perineural tumor compression of the nerve, then MRI should be performed to make a diagnosis, and if necessary, electromyography should be examined to further confirm and differential diagnosis. Third, other diseases: myofasciitis can lead to numbness in the left shoulder, accompanied by pain in the left inner scapula, so it is necessary to conduct physical examination to exclude other diseases for diagnosis and early treatment.