I have been a Crohns "sufferer" for 36 years,diagnosed after the birth of my identical twins.One of the twins was diagnosed with crohns when he was a teenager and the other one started with perianal abcesses acouple of years later.The doctors say that crohns is hereditary but there is no connection with the perianal abcesses but I dissagree and he has never been tested for crohns!!!
I was not familiar with "Perianal Abscesses" so I checked out a couple of sights. On one sight it did say that some people are more susceptible to perianal abscesses such as those that have: Diabetes, Aids or HIV, Crohn's or persons on medications that suppress the body's immune system, such as steroids (prednisone, methylprednisolone), or those undergoing chemotherapy for cancer ..........so I do not think that it is indictive of having Crohn's. The following is the website that I looked at:
http://www.emedicinehealth.com/anal_abscess/page2_em.htm
I have been operated on for an abscess (fistula) caused by my Crohn's disease,....after a hole perforated my bowel...and the abscess formed.....the way that my particular immune system looks after me......I had it drained.....I am now on a medication to prevent more....a medication called Purinethol:
Has your sister had any ultra sounds or cat scans done to see if she had Crohn's disease?