I have a similar problem. After being away from the saddle for 18 months, I did a 2 week offroad stint on a trip to the USA. The result was some kind of nerve damage (I think it's the median and to a lesser extent the ulnar nerves) in both hands, due to handlebar vibration/pressure. This was probably worsened by my overgripping the bars/brakes on steep descents (I'm a relative novice, and have a morbid fear of death) and, initially, badly positioned brake levers (too high).
I get some tingling / pins & needles in the little & ring fingers (classic ulnar nerve symptoms), but my thumb, forefinger and second finger were almost paralysed, especially on the left hand (rear braking?): it left me almost unable to tie shoelaces, hold a fork to eat, fasten my pants - you name it. I'm writing this two weeks later and I still can't hold a sheet of paper between my middle two fingers, and I can only just touch my thumb to my first and second fingers - I can't pinch at all. All this with no numbness and no tingling.
I think it was median nerve pressure at the base of the thumb, although my doctor seems to think I should have the classic carpal tunnel symptoms for this to be the case. If any doctors are reading this, I'd be grateful for other opinions.
After I recover (if), I'll be making changes to my riding setup, starting with lo-riser carbon bars instead of straight alloy ones, to change my wrist angles and adopt a more upright position (weight back on to the saddle). I'm also searching for a glove/mitt that has amazing padding at the base of the thumb. Specialized make a big deal about their Body Geometry gloves, but they really only seem to concentrate on the ulnar nerve area. All ideas gratefully received, and sorry to rambled gone on for so long!