I wonder how common this condition is for the regular lifter, one would have to train way beyond failure multiple times? I know crossfiters are proud of having it, stupid people.
Reading this I think I recall that at the very beginning, when I was working out for maybe 1 or 2 years, being probably severely overtrained as a young and over-motivated iron warrior

, I was getting my regular check-up at the doctor's office, and there was some protein found in my urine sample. The doctor (who had no clue about strength training though) told me that this was not normal because it meant that my kidneys had to clean Protein out of my system.
I never had any problems since then and didn't waste much thought about it, but maybe this was a small hint of the condition we're talking about in this thread.