Thumb twitching, also called a tremor, happens when thumb muscles contract involuntarily, causing your thumb to twitch. Twitching can result.
Shaking in your thumb is called a tremor or twitch. And it can trigger repeated muscle spasms called tics, which look like twitching movements.
Muscle twitching is caused by minor muscle contractions in the area, or uncontrollable twitching of a muscle group that is served by a single.
Two days ago my thumb muscle started to twitch when I relax my hand. I have no loss of strength and the twitching disappears as soon as I grip something.