Left arm and left leg numbness at the same time is common for the following reasons: First, cervical disc herniation, cervical disc herniation will compress the cervical spinal cord nerve, patients may show clinical symptoms of simultaneous numbness of the left upper and lower extremities, but usually there is no intracranial neuropathy caused by facial numbness, through cervical MRI will find cervical spinal cord nerve compression, cervical disc herniation. Secondly, patients may also suffer from cerebral hemorrhage, cerebral embolism and other brain diseases, which cause central nervous system dysfunction. Patients will show clinical symptoms of simultaneous numbness of the left upper limb and left lower limb, accompanied by reduced muscle strength of the left upper limb and lower limb, and even facial numbness and distorted mouth and tongue, etc. The lesions in the cranial cavity can be detected by CT scan or MRI scan. Therefore, patients with numbness in the left upper and lower extremities at the same time must pay great attention to it, and early treatment can provide a certain degree of relief of clinical symptoms, but sometimes it cannot be completely cured.