Don't suppose it's secondary dermatitis? I have that and was prescribed a steroid cream - betnovate - but the animal version used to be called vetsovate - it was so effective for just about anything that we used to call it 'magic cream' Now totally free of dermatitis, except a flare up occasionally then the cream goes back on and it's gone again. Maybe worth mentioning to your vet, handy stuff to have around anyway.