What Causes Rash Inside The Ankles While Having Psoriatic Arthritis In Toes?

I keep getting a red rash, that looks like a bad burn on the inside of my ankles, only on the inside of my ankles. I've been putting cortisteroid cream on it and it goes away, but it is taking longer and longer to go away each time. I am a 59 year old female with psoriatic arthritis in my toes and I also have another autoimmune disease, vitiligo. Family has a history of diabetes and every time I do a search, on the rash, diabetes comes up. Should I get checked?