The involuntary shaking of the left thumb is considered to be caused by chronic strain injury, cervical disc herniation and cerebral hemorrhage. 1. Chronic strain injury: Long-term use of the thumb or improper exertion or high-intensity use of the thumb can cause chronic strain injury to the joint capsule of the thumb, muscles, ligaments and other soft tissues, resulting in aseptic inflammatory changes such as oozing, edema and congestion, which can cause pain and weakness of the thumb, as well as involuntary shaking of the thumb and other symptoms. 2. Cervical disc herniation: rupture of the cervical intervertebral disc’s annulus fibrosus causes the nucleus pulposus to prolapse and break through the posterior longitudinal ligament, which can irritate and compress the nerve root, causing one or both sides of the upper extremities to suffer from radiating pain, numbness, and weakness, which can lead to the involuntary shaking of the left thumb. 3. Cerebral hemorrhage: trauma, hypertension, cerebral vascular malformation can cause cerebral hemorrhage, hematoma can compress the nerves, blood vessels, causing sensory and motor abnormalities, and may appear coma, respiratory distress and other serious complications. There are many other reasons for the involuntary shaking of the left thumb, it is recommended to consult a doctor for a clear diagnosis and targeted treatment under the guidance of the doctor.