--is thought to be mainly ischemic: that is, it results from the inability of smaller blood vessels, which are damaged by impaired glucose tolerance, to get oxygen and nutrients to the nerves and to carry waste products away. This is why the classic presentation of diabtic neuropathy is a slow onset progressive one, with "length dependency"--it takes time for the damage to occur, and it happens first to those nerves in the extremities farthest from the center of circulation. And, it can happen to anyone who has sufficient glucose dysregulation to have that ischemic damage. But, if someone has good blood sugar control, loses weight, increases circulation through exercise, etc., the circulation works better, and the nerve damage can be stopped or even reversed.

Variations in the intensity of symptoms--day to day or even over the course of a day--are very common with neuropathies, especially those of the smaller fibers that control the sensation of pain and temperature; many people report that it gets worse at night, for example (typically when circulation slows down).

Of course, impaired glucose tolerance is only one possible explanation. And it's likely Alan doesn't notice discomfort as much when he's active because his ciruculation has increased and there are other distracting sensations.

One thing that has also occurred to me, which I think you wrote about--Alan was given a workup for peripheral artery disease in his legs (which was negative), correct? Given his circulatory history that would certainly be something to be sure was investigated.