The most common cause of isolated finger twitching like this would be muscle strain
or muscle fatigue. This commonly occurs in people who work a lot with their hands, for example those who type on a computer keyboard all day long. The symptoms can usually be relieved by taking frequent rest breaks from work to stretch and by using ergonomically appropriate equipment as available. Twitching of a finger from muscle strain or fatigue is not a serious medical problem, and you would not need to worry about it.
On the other hand, if you have other symptoms in your hand, for example weakness of the muscles or numbness or tingling in any of the fingers, then these symptoms together could be a sign of a more serious nerve inflammation or compression, such as carpal tunnel syndrome
. Carpal tunnel syndrome typically causes symptoms just in the first three fingers of the hand (thumb, index finger, and ring finger). Many of the treatment options for carpal tunnel syndrome also include rest, just as for muscle fatigue, but anti inflammatory medications and splinting, as well as physical therapy, are also commonly used.
Start by talking again with your primary care doctor
to get your questions answered!