The conditions found in the rectum and sigmoid flexure in cases of chronic diarrhea differ very markedly, and they may be due to numerous causative factors.
They may be caused by a primary infectious agent, which may be an amebic, a bacillary or a flagellate infection, or some other infectious element which may persist over a long period of time.
The conditions may be due to the primary and some secondary etiologic factors, as when during the course of a proctocolitis, the primary cause of which was a bacillary or flagellate infection, the patient becomes infected with the pathogenic ameba. The case may be one primarily of amebic infection, which, though it has continued over weeks or months, or even years, may not have produced alarming symptoms, until some secondary infection ensues, which may convert a seemingly indifferent situation into one of alarm, with possibly fatal results.
JELKS JL. RECTAL AND SIGMOID CONDITIONS IN CHRONIC DIARRHEA. JAMA. 1917;LXIX(20):1671-1675. doi:10.1001/jama.1917.02590470011004