Hi, Welcome to JustAnswer. I am a licensed veterinarian and I'm here to help you. Poor Tilly! I understand that her skin condition is on her back and tail and around her anus. What you are describing are lesions. . ."round with a gritty looking scab". . .anything other than smooth skin we call a lesion. Is Tilly itchy. . .licking more than normal or scratching with her legs?