I only have CD in the rectum. I got an abcess and fistula but no other symptoms. If it weren't for the abcess, I wouldn't have known I had anything. I'm on Remicade now, and my colo-rectal surgeon says the lesion in the rectum has healed ( I have a seton through the fistula... will fix that later). CD can attack the tissue of the rectum very deeply. I'm wondering if this may be what you are experiencing.
There aren't many of us who have CD only in the rectum. I'd be interested in hearing about your experience with CD.
Hope your symptoms clear up very soon!
This is taken from this website: http://www.nlm.nih.gov/medlineplus/ency/article/003131.htm
Tenesmus is the constant feeling of the need to empty the bowel, accompanied by pain, cramping, and involuntary straining efforts.
Tenesmus is generally associated with inflammatory diseases of the bowel, which may be caused by an infection or by other conditions. Tenesmus is characterized by a sensation of needing to pass stool, accompanied by pain, cramping, and straining. Despite straining, little stool is passed.