If a patient suddenly develops weakness in one leg, most of them are caused by cerebrovascular diseases. It is usually seen in lesions of the brain, including cerebral hemorrhage and cerebral infarction, and cranial CT examination can make a clear diagnosis. If a patient suddenly develops weakness in both legs, it may also be due to cerebrovascular disease, which is usually seen in brainstem lesions, including brainstem hemorrhage and brainstem infarction. If there is a lumbar disc herniation, it may also be easy to compress the lumbar medulla, and the patient may experience weakness in both lower extremities, as well as sensory disorders including numbness, wood, and pain below the lesioned segment. In severe cases, urinary and fecal disorders, urinary and fecal incontinence, and urinary and fecal retention may occur, and if necessary, lumbar spine MRI should be examined to clarify the diagnosis. It can also be seen in myasthenia gravis periodic paralysis and Grinbaris syndrome. Patients with myasthenia gravis usually have milder symptoms in the morning and more severe periodic paralysis in the afternoon. Most of them are caused by low blood potassium and the patient usually presents with proximal muscle weakness. In the case of Guillain-Barre syndrome, it usually presents as distal muscle weakness, and most patients have a history of viral infection prior to the disease.