VSL#3 is a probiotic. You can read more about it here: http://www.vsl3.com . It is pretty expensive, but if you compare all the probiotics on the market, it has the highest payload (450 billion bacteria). Also, a small clinical trial showed that it is as effective as asacol (oral 5-ASA medication) at putting and keeping people with ulcerative colitis in remission.
Your doctor is correct in stating that the course of this disease is unpredictable. However, there are things you can do, to try and control this disease. We prefer to not take a fatalistic attitude towards this disease (your doctor needs to encourage you to do everything you can to keep yourself healthy and to not be so fatalistic). Folks here on the board recommend "treating both ends" - ie. taking oral 5-ASA medication (like Asacol) and suppositories/enemas (Canasa/Rowasa), to keep things under control. The idea is that you may help prevent proximal spread of the disease by pre-emptively taking oral medication as well as suppositories to keep things calm in your colon. However, my husband did not like the idea of taking additional medication (even though I've heard Asacol is usually fairly gentle). Since we read that VSL#3 is as good as Asacol at putting and keeping folks in remission, we decided he'd take VSL#3 (which doesn't really have any side effects). VSL#3 (in large doses) may have the same effect as taking Asacol (of course this isn't proven, and only a small clinical trial validates this). Other folks on this board use other probiotics such as Culturelle, Acidophilous pearls, etc. In general, it's a good idea for folks with Ulcerative Colitis (or Proctitis) to take probiotics and eat a lot of yoghurt.
A lot of bacteria live in your colon, and form the flora of your colon. One theory of IBD is that folks with IBD have an imbalance in the bacteria in the colon (whereby there is an over abundance of bad bacteria and not enough of good bacteria) and this eventually causes the mucous barrier in your colon to bread-down, resulting in the bad bacteria adhering directly to the colon wall, resulting in an immune reaction that causes ulceration and inflammation of the colon. Understand that I'm not a medical genius - this is just my understanding of the theory. The exact mechanism of how the bad bacteria result in inflammation is not yet understood. However, one thing I've always noticed is that anytime my husband eats or drinks anything sweet, he has a lot of gas (produced by the bad bacteria in the gut). So, it wasn't a stretch to believe that controlling his diet to eliminate unnecessary sugars, starch, and caffeine would help him (which it has - he is far less gassy, and his bowel movements are a lot more regular, and his stools are well formed and easy to pass).
When my husband was first diagnosed with ulcerative proci***, our GI didn't alert us to how serious this disease can be. He just said, take canasa and cortifoam (for a short while to get things under control), and continue to take it and you'll be fine. When first diagnosed, my husband took canasa nightly to get things under control, and then slowly tapered to once every other night and finally to twice a week. His doctor did tell him that he can never completely stop taking canasa. My husband had his second flare in april 2006, and this time his symptoms were a lot worse than the first time (plus we didn't recognize symptoms of a flare - we thought it was an infection, or something like that, so it took a while to treat it). He had to take prednisone to get the flare under control, and has since then remained on canasa nightly. We may try to start tapering to once every other day next year.
When in a flare, our doctor recommends a low residue diet. Like just plain white rice and chicken, plain pasta and chicken, etc. The reason is that the "roughage" (fiber and bulk that veggies can add) can irritate the colon (and since it's already ulcerated, it can hinder healing). He said when not in a flare, my husband could pretty much eat anything. However, after a lot of the reading we've done, we've decided to limit his sugars, add more whole grains (brown rice, whole grain bread, etc), and eat a lot of yogurt. I think in general, we are a lot healthier than before (myself included).
When my husband was flaring last year, he had difficulty keeping most food down, and was fast losing weight. We tried the SCD (Specific Carbohydrate Diet) to see if he could get more nutrition with it, and it really did help him. He had a lot of gas pain after eating, and the SCD helped keep the gas down tremendously (because you don't really eat very many carbs with the SCD). We find that taking the VSL#3 has a similar effect to the SCDiet in terms of gas reducation. If you're having trouble with lot of gas pain, and getting effective nutrition from your food during a flare, I would recommend trying the SCDiet. There's lots of information about the SCDiet if you search for it online.
Your doctor has given you the correct information - that the course of this disease is different for each person, and that despite your best befforts, the proctitis may spread to become even pancolitis. It seems that he's got you on the right medication right now to get your flare under control. You will likely have periods of remission and periods of flares, or you may never have another flare. From what I read, most people believe that proctitis for the majority of people doesn't spread proximally. However, another study I read said that the chance of proximal spread for the disease was about 50% at 10 years (but of course a statistic is just a statistic until it happens to you). For us emotionally, it was difficult to accept that he's got a chronic disease that can have such an unpredictable course - only time will tell how this will affect your life. The only thing you can do is to learn more about this disease and do your best to do the right things and try to control the disease. This forum is a great place to do that, so I think you're on the right track.
One other piece of advice I have for you is to always be conscious of your body - if you have cramping, stomach pain, your stools get narrow, or you get constipated, or you have a little mucous in the stool, or you have a spot of blood, etc. The best way to control a flare is to treat it at the first sign of problems. I'd make sure that you have a prescription for canasa and the cortifoam always available, and learn how to adjust your dosage as your body indicates. Of course this is trial and error, and you'll just get better at this the longer you have the disease. Also, do not take anti-biotics, or asprin or any non-steroidal anti-inflammatory medicataion, becaues they can worsen your UC. Tylenol is ok. If you have to take antibiotics, consult your GI to determine which antibiotics are safest for people with UC, and take a lot of probitoics when you take these antibiotics.
My husband also takes fish oil suplements and a daily multi-vitamin, in addition to his VSL#3. So far this stuff seems to be working for my husband, but of course that could all change tomorrow. I wish you a speedy recovery. I hope you have a better grasp now of this disease.
Husband with Ulcerative Proctitis
Diagnosed March 2003, 1st Flareup after diagnosis Apr 2006
Currently in Remission
Nightly 1000mg time release Canasa
Even though he has no symptoms, he's on VSL # 3 (1 packet daily) for prevention
Was on the SCD, but we stopped after 4 months of no symptoms - he's doing fine on a normal diet