The sudden onset of numbness in the left arm may be caused by two things: cerebrovascular disease and cervical spondylosis. If an elderly person has risk factors for cerebrovascular disease, such as hypertension, diabetes, hyperlipidemia, hyperhomocysteinemia, cerebral atherosclerosis, smoking and alcohol consumption, and other poor lifestyles, sudden onset of left arm numbness must be alerted to cerebrovascular disease, and must promptly consult the neurology department of the hospital for physical examination and head CT or magnetic resonance brain imaging to clarify whether there are acute cerebrovascular problems. We must promptly consult the neurology department of the hospital for medical examination and head CT or magnetic resonance brain imaging to clarify whether there are acute cerebrovascular problems, and then carry out symptomatic treatment. The second point to consider is caused by cervical spondylosis, sudden left hand and arm numbness if caused by cervical spondylosis, must be in a good posture after a long time, need to consult the orthopedic department for cervical spine examination, can be traction, massage and other ways to relieve.