Muscle twitches are minor and often go unnoticed. The causes of thumb twitching are Carpal Tunnel Syndrome, Complex Regional Pain Syndrome and Amyotrophic Lateral Sclerosis. It can also be caused by genetic compositions or can be the beginning of some types of epilepsy or Parkinsonism. Other common causes are Diet deficiency, drug overdose, benign twitches or side effects of any Drug. You need to seek professional help. Consult a neurologist. You may need tests like urine tests, blood sugar level tests, nerve conduction tests etc.Do write to us again. Hope it helps.