The causes of double lower extremity muscle weakness are hypokalemic periodic paralysis, acute cerebrovascular disease, motor neuron disease, spinal cord lesions, etc., which are as follows: 1, hypokalemic periodic paralysis: if a young patient develops double lower extremity weakness with acute onset of the disease, ask the patient whether there is any binge drinking or large amount of alcohol on the previous day, and carry out potassium monitoring to find out whether there is hypokalemic periodic paralysis; 2, acute cerebrovascular disease: if an elderly patient has previous risk factors such as hypertension and diabetes, and then suddenly develops double lower extremity weakness, carry out cranial MRI to find out if there is any acute cerebrovascular disease, such as cerebral infarction or acute diabetes. Acute cerebrovascular disease: If the patient is an elderly patient with previous risk factors such as hypertension and diabetes mellitus, and sudden weakness of both lower limbs occurs, a cranial magnetic resonance examination should be performed to find out whether there is acute cerebrovascular disease, such as cerebral infarction or acute cerebral hemorrhage; 3. Motor neuron disease: If the disease course is slowly progressive, accompanied by muscular dystrophy, a cranial magnetic resonance, electromyography, and lumbar puncture examination should also be performed to find out whether the patient has motor neuron disease; 4. There is no motor neuron disease; 4, spinal cord lesions: patients with bilateral lower extremity muscle weakness, we must ask the patient whether there is low back pain, whether there is dysfunction of urination and defecation, if there is, we must carry out lumbar or thoracic spine magnetic resonance examination, to understand whether there is spinal cord lesions.