Ok, now........I'm going to TRY to help you feel less anxious about the brain shrinkage issue.
Brain shrinkage isn't only associated with MS, as you are finding. So far, there are findings that it shrinks from social drinking, ADHD, depression, some mental diseases (i.e. schizophrenia), from some medications, and it just plain can shrink as you get older. And as you just found, it can even shrink from pain, apparently.
A lot of people can have MS for many many years, and their brains don't shrink at all.
Had you not been diagnosed with MS, would you be as concerned about your brain shrinking, or would you have never given it a second thought (and your brain might have shrunk anyway and you would never have known it)?
I'm certainly not trying to diminish your concern, but I also hate to see you overly concern yourself about something that may never come to pass (you know I care and even worry about you and others quite often), and even if it does, how will you know from which association/condition that it shrunk as a result of?
On the other side of the coin, in doing some other research today regarding axons, I did run across some interesting information that it is believed now (by some researchers) that brain shrinkage (atrophy) from MS is most likely due to some degeneration or shrinkage of the axons in the brain, and not from any loss of pure "brain cells".
Also, I read additional information that says lack of physical exercise will cause your brain to shrink, which again could be associated with MS due to decreased physical activity (as or if you become physically impaired).
On the other side of the coin again, you CAN also increase
your brain size (believe it or not) by doing mental exercises (thinking and doing crossword puzzles, etc.) and by incorporating as much physical exercise as is reasonable for your particular physical condition.
Now........having said all that, I hope you take from my comments that you are not simply at the complete mercy of brain atrophy or shrinkage due to MS.
I believe there is quite a bit that you can do to counter-act it.
EDIT: You are not going to believe this, I just now found that jet-lag causes brain shrinkage, also.
SECOND EDIT: Oh....geez.....I forgot to mention that some medications have even shown indication of either arresting or reversing brain shrinkage.
OK...here's a quick excerpt from an article that I just grabbed real quick to help show what I'm talking about (and what you've seen Robin and I banter about regarding "plasticity"), but there are many other articles and research abstracts that you can locate that substantiate all this, too:
http://www.healthandage.com/html/min/af ... her6_2.htm
On the bright side, the brain has a great capacity for adaptation, modification, and repair. The term plasticity refers to the ability of the brain to modify its structure and function. This capability continues throughout life. For one thing, there is a certain amount of redundancy in the brain. If one network of neurons is damaged or dies, another network can take over the function. The death of neurons can also be compensated for by surrounding neurons sprouting new connections to take the place of the lost ones.
The brain is a dynamic, not a static, system. The neurons respond to mental stimulation and environmental factors. And there is the capacity to respond to age-related changes. It appears likely that cognitive changes are noticed at a point when the compensatory mechanisms of the brain are unable to overcome physical changes taking place. There may be strategies, either with medications, mental exercises, or something else, to enhance the brain's natural capacity for plasticity and thus forestall cognitive declines associated with aging. ...."