What could cause chronic white knuckles?

Knuckles only . Some possible answers: vitiligo, leucoderma, post traumatic, post inflammatory skin conditions. A dermatologist can help you with this.
White knuckles. The reasons for white knuckles are many. If the skin is thick or scaling it may appear white when the fingers are slightly flexed. If the knuckles are white when the fingers are straightened it maybe decreased blood in the area especially if the fingers are swollen. Anemia can also cause white knuckles when the fingers are bent.