--are fairly common with small-fiber/autonomic neuropathy, and part of the reason why some physicians suspecting these will order th sudomotor axon reflex or other sweat tests, to see if the small, unmyelinated nerves that control the opening/closing of sweat pores react as they should with temperature fluctuation.

See:

http://neuromuscular.wustl.edu/auton...#hyperhidrosis