Pain in the base of left thumb...

[dss]

Sometimes, not always, I will get a severe , stabbing pain at the base of my left thumb (near the wrist) somewhere near transition from backswing to downswing. I cannot hold the club or even think about the shot; I just quit and usually hit a dribbler. The area will ache like a toothache for awhile, and be sore for days. I played yesterday, and had only one painful episode (on the range warming up). Today, my wrist is sore at the thumb base area. I wore a brace all day at work (seemed to help). Has anyone ever heard of this? Any suggestions would be welcomed...thanks.