hi and thank you. pleased to answer you. At night, the female adult parasitis deposit their eggs outside the rectum or anal area, and they will generate itching in the crack in your buttock. tape test or scotch test made on that region can gave valuable information for the diagnosis. Firmly press the cellophane tape over the anal area for a few seconds. The eggs stick to the tape. The tape is then transferred for eggs parasites analysis. I think that this test is the first thing to do before . Pruritus (itching) may have no cause, it is then essential: it is pruritus disease with a psycho-somatic dominance. Dermatosis when it exists is the consequence of scratching which can lead to secondary superinfection. when no causes are found in cases of pain and itching buttock it is important then to do a complete digestive assessment, especially colo-rectal because it may be a sign of an anal or recto-colic diseases including tumor. may this help you and best wishes