The causes of numbness in one arm and leg are as follows: First, if it is sudden, it can be clinically seen in cerebrovascular diseases, cerebral hemorrhagic diseases such as cerebral hemorrhage, subarachnoid hemorrhage, ischemic diseases, cerebral infarction, transient ischemic attack, cerebral embolism, etc., which can be diagnosed after CT or MRI examination of the head, and treatment should be given to the hemorrhagic and ischemic lesions. Second, if it appears slowly, it can be clinically seen as intracranial occupying disease, and the lesion can be found after CT or MRI of the head. Numbness in one arm and leg can also be seen clinically in patients suffering from cervical spondylosis and lumbar disc disease at the same time, and numbness in the arm and leg can be confirmed by CT examination of cervical and lumbar discs due to compression of nerve roots by the protruding cervical and lumbar discs.