I too am looking at several crescent shaped discolorations under the skin near the nail. One extends to the cuticle. They have the same appearance as scar tissue on other parts of my hand like an oven burn or old scratches. Wonder what they are?
It is indded hard to explain. I'm having trouble picturing it, especially the part about the whiteness extending beyond the nail onto the thumb . . . ? Also, you don't say how long it's been there.
I think you ought to show the condition to a doctor.
Best.
Dr. Rockoff