What Causes Dark Spots Of Forearms While On Estrogen Blocker?

This past year I seem to be experiencing darkred spots on my forearms, I am fairly thin skinned and am an estrogen blocker, would this cause spots? I did go to a dermatologist and she called it something senile....which I had to laugh at...I am 69, very active, have exercised for over 35yrs....don t like these spots, remind me of my very elderly grandmother.