--diabetes not be considered as a possible cause, since it, and even impaired glucose tolerance short of frank diabetes, are well-known common orginators of neuropathy?

And, you didn't go into great detail about your lower back situation, but if imaging shows any sort of nerve root compromise, that could certainly be a contributing factor as well. In fact, both may be contributing in what is known as the "double crush hypothesis"--already metabolically or chemically damaged nerves are then further insulted by compressive forces, and are more prone to symptoms from them, with the symptoms being additively out of proportion to what one would assume the combined effects might be.