Age and damage-related arthritis. Osteoarthritis I guess.
I've had sore joints before and put it down to 'start of age-related arthritis'. That has waxed and waned a bit.
This time, no doubt. Little finger joint starting to swell, painful all the time. Although it is my strong (and not-so-damaged) hand, I'm finding excuses not to use it.
It is surprising how discouraging mild, but chronically persistent, can be. Dammit, I still have a lot I want to do!