My hands swell slightly and feel stiff when I get dehydrated. I don't like the taste of tap water so in the past I rarely drank water...so this happened a lot throughout my life. The swelling was never enough to cause problems, but I have learned how to make it go away. Drink water! I experienced this hand stiffness more when I started taking Mestinon and have finally developed a habit of drinking water regularly. No hand swelling/stiffness with plenty water.

This may not be what is happening with you, but I hope this helps.