Involuntary tremor of the left thumb may be caused by physiological factors, but also idiopathic tremor, hyperthyroidism, Parkinson’s disease and other diseases. 1. Physiological factors: mainly associated with nervousness, emotional excitement and other reasons leading to sympathetic nerve excitation, the emergence of involuntary tremor of the hand symptoms, when the emotional stability of the natural disappearance of the symptoms. 2. Disease factors (1) idiopathic tremor: at the onset of this disease, patients often experience involuntary tremor of the fingers of the left thumb when they are tired or emotionally agitated, and the symptoms of tremor can disappear after doing random movements. (2) Hyperthyroidism: This disease is caused by excessive secretion of thyroid hormone, which leads to increased metabolism and may result in involuntary tremor of the fingers of the left hand. (3) Parkinson’s disease: This disease is common in elderly patients and is mainly caused by the lack of dopamine in the basal ganglia. At the onset of the disease, there will be involuntary tremor of the left thumb, accompanied by increased muscle tone. When involuntary tremor of the left thumb occurs, you should go to the hospital in time, under the guidance of the physician, to clarify the cause and then give targeted treatment.