I think in your case that your doctor should be able to tell you if cycling will aggravate your condition. If not, then you need to get cycling both to get fit and to see if you really will be OK on tour.
A back injury I sustained falling on the GDMBR last summer dogged me from Yellowstone to Antelope Wells, and an injured achilles heel continued to pester me for 6 months after the tour was over. Injuries, sustained either before or during one's trip can definitely affect the level of one's comfort.
This year I had to postphone my trip (San Diego - Vancouver - San Diego) due to surgery (and the Gordo slide), but I have the flexibility to wait: conditions will be better later anyway. But I'm anxious to get going. My doctor knows my plans and used thicker sutures when he sewed me up. I'll be back on the bike tomorrow, seven days after surgery.