Left arm numbness should be alert to frozen shoulder, diabetes, cervical spondylosis, peripheral neuritis, carpal tunnel syndrome, elbow tube syndrome, etc.. 1. Diabetes mellitus: If the patient suffers from diabetes mellitus, it leads to peripheral nerve lesions, resulting in numbness of the left arm, accompanied by symptoms such as polyphagia, polyuria, etc. The patient may also suffer from cervical spondylosis. 2. Cervical spondylosis: due to long-term strain on the cervical spine, osteophytes, ligament thickening, etc., resulting in the phenomenon of numbness in the left arm, accompanied by pain and stiffness in the back of the neck and other symptoms. 3. Peripheral neuritis: this disease is mainly caused by infection, nutritional disorders, endocrine disorders, etc., patients will have numbness of the left arm, accompanied by sensory and autonomic disorders. 4. Carpal tunnel syndrome: If there is fracture and dislocation of the carpal bone, sprain and contusion of the wrist, chronic injury of the wrist, etc., it will reduce the volume of the carpal tunnel, increase the pressure in the lumen, and compress the median nerve, and numbness of the left arm may occur. 5. Elbow tube syndrome: when the ulnar nerve is pulled due to postural abnormalities, fractures, tumors, malformations, cysts, etc., it will make the patient experience numbness in the left arm. It is recommended that patients go to the hospital in time, under the diagnosis of the doctor, according to the patient’s specific condition, to take targeted treatment.