Firstly, I must admit that I have been lurking on this site for well over a year and now your story has motivated me to register so that I could respond to your post. I cannot imagine the challenge you faced in having that conversation with your son. When my daughter was 4 or 5 the pediatrician referred us to a "specialist" to have a lump looked at. Turned out to be nothing, but I have never felt so helpless as I did for that period of time between the referral & the actual appointment.
I was DX in April 2004 at the age of 38. The route to DX was atypical in my case in that it took only 3 months. I did not experience any of the emotional distress that is typically associated with such a DX. I was actually quite relieved to know what was going on with myself.
When I told my Mother of the DX she, of course, inquired about my symptoms (one of which is a slight intention tremor)-Mom's reply: "You were doing that when you lived at home" (20+ years prior). Her observation has led me to the belief that MS has been with me for most of my life, I just did not know it. Looking back, it all made sense. I have discussed this with my Neuro & he agrees that I may have a mild form of MS that took many years to get my attention.
Of course, this may have little or no relevance to your son's situation because everybody is different (bet you've read that 1,000 times). I would like to offer this advice: Be Honest with your son, Learn all that you can & share this with him. I would also suggest that you teach him to keep a journal of symptoms. I bet you have read that 1,000 times also. I have never been able to do this consistantly and I know that it would be helpful at Dr. appointments. Your son has the advantage of learning it young, His Journal, His Notes (Not Yours-you keep your own).
1. You already know he does not tell you everything-it is much easier to write it down than to tell your mom, (don't get upset mom, it's a guy thing)
2. Teaches him good habit for future Dr. visits. (You won't be joining him at Dr. office forever mom, it's a guy thing.)
3. It will empower him. (He is doing something about his situation.)
I agree with your instincts ("I don't want to whisper around him"). Be as honest as you can, be hopeful, be positive. But, be honest with him.
I'm on Avonex. It has worked well for me thus far. That decision was base on the fact that it is once a week. The needle is intimidating, but the injection is really not that bad. I have done it myself, but I usually get my wife to do it (I am intimidated & not afraid to admit it!). She has gotten quite good at it, as I barely feel it most of the time. The side effects were bothersome at first, but lessen with time. Hope this helps.