Causes of numbness of the corners of the mouth and arms include cerebral infarction, intracranial tumor, autonomic dysfunction and so on. 1. Cerebral infarction: it often occurs in middle-aged and old-aged patients, due to cerebral ischemia, the sensory conduction of the brain is impaired, causing numbness of the corners of the mouth and arms, which can be examined and diagnosed by cranial CT or MRI. 2. Intracranial tumor: if suffering from intracranial malignant tumor leading to the damage of sensory center, patients may have the symptoms of numbness of mouth corner and arm, which can be examined and diagnosed by cranial MRI and so on. 3. Autonomic nerve dysfunction: there are many symptoms at the onset of the disease, and patients may have numbness of the corners of the mouth and arms, as well as dizziness, chest tightness, palpitations and other symptoms. Patients with numbness of the corners of the mouth and arms must go to regular hospitals for diagnosis and treatment.