Hi, My Husband Has Ring Worm Like Circles Across His

Hi, My husband has ring worm like circles across his back (between his shoulders).
Our local doctor said he hasn't seen anything like it before and prescribed some very expensive cream to be applied 4 times a day. That was 2 weeks ago and it hasn,t helped.
It isn't itchy at all and doesn't bother him, but he is a little concerned because they have spread since I last noticed them about 3 weeks ago.