Proctitis does not cause thinning of stools. Proctitis is usually an inflammation in the rectum, and it is more common for the patient to have more frequent stools, that is, diarrhea, 2-5 times a day, and possibly blood in the stool, bright red or dark red blood, which does not cause the patient to have thinning of stools. The phenomenon of thin stool should be due to a mass in the rectum, such as colorectal adenoma or rectal cancer, which leads to narrowing of the intestinal cavity, so that the phenomenon of thin stool can occur. You can first perform anorectal diagnosis to palpate the mass, or perform colonoscopy to find out whether there are lesions inside the rectum or the whole colon, and if necessary, take pathological examination to clarify the diagnosis.