I have no idea. I read about them vanishing on another forum, and subsequently noticed mine had gone.
I wouldn't have noticed if it hadn't been suggested to me.
I get pin-prick pits in them sometimes, and they have gone very striated - vertical ridges from root to tip.
The most peculiar thing that has happened to my fingers is complete loss of elasticity in the pads of my fingers.
If I press my thumb and forefinger pads together for a short while, then remove the pressure, I have great big dents in my pads for a long time.
I tried to time it once, but gave up after an hour - the big dent was still there. My thumbs are the most "impressive"

.
I suspect it has to do with an ME-related general failure of elastin and collagen....