There are many causes of numbness in the arm, the most common are cervical spondylosis, brain lesions, trauma to the brachial plexus nerve, etc., as follows: a. Cervical spondylosis: if the patient has cervical spondylosis, common neurogenic cervical spondylosis, when the nerve root is compressed, it will lead to the clinical symptoms of numbness in the arm all the time, the need for cervical spine CT, MRI examination, can be clearly diagnosed. Second, brain lesions: patients with brain lesions, common brain hemorrhage, brain tumors, brain contusions, cerebral infarction, will also lead to the presence of clinical symptoms of numbness in the arm, the need for cranial MRI, can be clearly diagnosed. Third, brachial plexus nerve injury: when the arm is traumatized after causing damage to the brachial plexus nerve, will also lead to the presence of clinical symptoms of numbness in the arm, the need for electromyography examination, can be clearly diagnosed.