There is no such thing as numbness in the left index finger to alert you to four diseases. The numbness of the left index finger may be caused by physiological factors, but also cervical spondylosis, carpal tunnel syndrome, and cerebral infarction and other diseases. 1. Physiological factors: patients may be due to sleeping posture improper factors such as prolonged compression to one side, both arms and fingers, resulting in blood circulation disorders, may appear left index finger, left hand numbness symptoms. 2. Cervical spondylosis: cervical spondylosis is mainly caused by long-term strain on the cervical spine, osteophytes, herniated discs, thickened ligaments and other factors. When the nerve root is compressed, the patient will have neck pain, unilateral or bilateral upper limb numbness, weakness, nausea and other symptoms, resulting in the patient may appear in the left index finger numbness symptoms. 3. Carpal tunnel syndrome: Carpal tunnel syndrome is caused by factors such as exogenous compression, carpal tunnel becoming smaller, and occupancy in the lumen of the canal. The main symptoms of patients are abnormal sensation of thumb, index finger, wrist, finger pain, muscle weakness, etc., which can lead to numbness of the left index finger. 4. Other: cerebral infarction, multiple peripheral neuritis and other diseases may also lead to numbness of the left index finger. Numbness of the index finger of the left hand may be caused by physiological factors, generally do not need treatment. If it is caused by disease, patients should seek medical treatment to identify the cause of the disease and treat the symptoms.