The causes of numbness in the left thumb and index finger are the following: 1, due to cerebrovascular accidents, cerebrovascular accidents include cerebral infarction, cerebral hemorrhage and other diseases, this disease can be clearly diagnosed through CT or nuclear magnetic examination. If there is a cerebrovascular accident, there will be numbness in the fingers, arm weakness and other conditions, should take timely treatment measures to deal with. 2, the left finger numbness may also be caused by cervical spondylosis, the nerve root of the upper limb is in the neck, if there is a serious cervical spondylosis, compression of the nerve root will appear after the left finger or index finger numbness, as well as arm weakness and other conditions, through the film examination can be diagnosed. 3, the left thumb The numbness of the left thumb or index finger may also be caused by carpal tunnel syndrome and elbow tunnel syndrome. This disease is mainly due to long-term physical work, resulting in carpal tunnel or elbow tunnel syndrome, which can be diagnosed by doing electromyography, and once diagnosed, treatment measures should be taken.