I have this type of fistula. Mine is caused by Crohn's disease. From my understanding from what my doc told me is that it really depends on the person and the meds being used. I take asacol for the Crohn's, that has helped some but not a lot. My doc wants to put me on this medicine called remicade it is suppose to help a lot with fistulas. I dont want the meds becouse I am hoping to have children pretty soon and they can not tell me enough about it to make me feel safe taking it when I could become pregnant. My fistula were found by a colonoscope after I insisted there was something wrong "down there". Well I hope this helps a little.