It's interesting that statistically (this from memory) only in about
20 to 30% of those initially diagnosed with proctitis does the disease progress further. So the answer to your question is, absolutely it can and ussually does remain as proctitis. Anecdotally, on this forum, it appears to be a much higher %, I am one of those in which it progressed. All the info one reads says that it is much better for the long term prognossis (cancer risk etc.) that UC remain in the rectum. It certainly is easier to treat with drugs applied directly to the effected areas rather than systemic meds. My personal experience was that from a symptomatic point of view a flare or even moderate inflammation in the rectum caused me more problems, urgency issues in particular, than later when the UC spread upwards.