Billy,

I know we have discussed Sjogren's with you before...and you are trying to look beyond since you have negative tests.

Just so you know, the small fibers of the peripheral nervous system, not only control pain, touch, and smell, but they also control/affect the autonomic nervous system. That autonomic system can cause changes in heart rate, BP, urinary and GI function, AND even the moisture producing glands in the mouth and eyes. So YES, you are correct in the SFN alone can cause the dry mouth and eyes.

The joint pain may be from another cause, like general arthritis or maybe changes in the moisture of the synovial fluid in the joint...causing more painful movement.