My mother (age 97) has a rash on her thigh that started out looking like a pimple that, within a week or two, grew to the size of a dime . It developed small dark red pustules around the outer edges, which after a few days released pus, causing a crust which she cleansed off. The rash started looking better, but the next day it broke out again, with small dark red pustules around the outer edges. This cycle has been going on for over four months now, continually widening the ring with each outbreak. It itches, stings, and burns, and is very painful. Three doctors have looked at it and can't figure out what it is. Topical and oral antibiotics haven't helped the rash at all. It is also erupting in other places on her body.