Suggest Treatment For Infection In The Nail

Hi For about 4 years now I have what my dermatologist called nail dystrophy. It affects both of my thumbs with horizontal lines in the center from bottom to top. I believe it was caused by an infection to the area(I had also on a small finger) the small finger had no damage to the nail but the thumbs did. My dermatologist first said is was due pushing down the cuticles(which I have done for years) due to a nervous habit. I am puzzled because it happened after I had dryness and infection. Nothing I tried has changed the condition. My dermatologist believes my nail beds were affected and that their is no solution. What do you say??? Thank you! and