Sudden weakness of the lower extremities and inability to walk, if the lower extremities are unilateral, consider acute cerebrovascular disease, generally monoplegia in cerebrovascular disease is also relatively common, the site will be in the parietal lobe. For example, if the weakness of the right lower extremity cannot walk, the lesion may be in the left parietal lobe, so it is necessary to promptly consult a hospital for head MRI or head CT examination, and then give symptomatic treatment after the neurologist’s examination and clarification of the disease. The weakness of the lower extremities of a single limb may also be caused by lumbar spine disease, but the patient should have a past history of low back pain and symptoms of lumbar disc compression, which will not start suddenly. If the lower limbs are weak and cannot walk, the patient may have hypokalemia.