Tiny veins appearing while taking HU for Essential Thrombocythemia

I have been on HU for Essential Thrombocythemia since the first part of November with good results. My platelets have fallen from the mid 600s to 398. Over the last month I have had tiny veins appear and disappear on the back of my hands. They are slightly raised and sting or itch slightly. Now I have one on my knee. Has anyone else experienced this?