Hi I Had A Certain Growth On Screen ( Black

Hi i had a certain growth on screen ( black in colour) along with some corn like growth on the foot the doctor had prescribed sorvate C cream from glenmark for that. What is this exact disease I had got hypothyroid which causes dryness to the skin along with some diabetic condition ( not severe ) only one tablet of Glycomet a day is prescribed. Is it some scar due to which the lower skin is exposed and the top layer of the skin is destroyed or some kind of serious problem. These black growth on skin itches only in night and for the day it is normal and with no itching.