Contact dermatitis, insect bite all can cause red itchy rash on the ankle
but swelling is unlikely in these conditions. Ankle
swelling can be seen in rheumatoid arthritis, reactive arthritis, osteoarthritis, gout.heart problems, kidney ailments etc. In gout the joint appears purple, shiny, feels very sore and tender, and is inflamed/swollen. Seek medical help. Treatment will depend on the cause. Do keep me posted.
Take care and regards!