I'm not familiar with cubital tunnel syndrome. I haven't seen itch from swelling alone in carpal tunnel syndrome either.
While I'm not sure what's causing your itch, it doesn't sound as though you have eczema or some other primary skin condition that would be visible.
I suggest continued use of Sarna, keeping the elbows covered at night to minimize scratching, and seeing a doctor if the matter persists.
Take care.
Dr. Rockoff