What Could Cause Weakness In A Few Fingers Of The Left Hand?

60y/o/ Latino Male in overall good health. But recently experiencing some weakness (no numbness or pain) in L thumb and index finger x 1 month. No trauma to Left side extremities. Had Neuro exam, CT Scan, EKG, bloodwork to R/O CVA or AMI. (results Negative). Xrays to L side extremities ( ALL negative). I do have Neuro F/U in 6 weeks but this is alarming to me because this is my dominate hand. what do you think my condition might me. I did not get an answer from my MDs. help