Did you examine and inject any of these folks?
I should probably clarify what I said-- these are the cases for which no alternative answer was found. For most of the cases fitting the "discogenic" pattern, I take them back for a shot-in-the-dark epidural and before finishing do an exam under fluoro. Very often the pain is focused over the L5 spinous process or uni/bilateral PSIS, and goes away with a quick diagnostic TP. Now unless specifically asked to do an ESI, I will often take these folks back to do diagnostic TPs under ultrasound. They often get much better with 1-2 procedures.
Re: Chemical radiculitis
I believe I have experienced this myself. At the insistence of my wife I was doing a bridge over an exercise ball and felt a crack in my back. It didn't hurt at the time, and I figured maybe I just crunched some interspinous ligaments, a facet joint, or something. The next day I noticed a spot on my ribcage just below the nipple no larger than a quarter that felt like it was sunburned, but only when I touched it. This took 3 weeks or so to resolve. I never had any "shooting" or "radiating" pain all the way around the chest. Just that one spot. Hasn't come back since.