Numbness of the left upper limb is usually diagnosed and prognosis assessed by electromyography, which is relatively common in clinical practice. The cause of numbness in the left upper limb may be single nerve damage (e.g. radial nerve, ulnar nerve damage), peripheral nerve disease (e.g. diabetic peripheral neuropathy, alcoholism, etc.), spinal cord disease (e.g. spinal cord occupancy), etc. Electromyography can be performed under the evaluation of a physician. During the test, the muscles to be examined are selected, and by analyzing the electrical potential patterns generated during muscle activity, it is possible to locate the damaged nerves, identify the location of the lesion, perform a differential diagnosis of the cause of the disease, and determine the severity of the patient’s lesion, which helps to assess the patient’s prognosis. Electromyography is an electrophysiological examination, and in the treatment of disease, the necessary auxiliary examination is very important, to clarify the cause of the disease, and the treatment of the cause, in order to obtain as good a prognosis as possible.