I always thought that it was an MS related thing too because I've had it for about as long as the MS (DXed in 1978), but only a few of my fingers have been affected.
I'm not sure if there is anything that you can take for it but it might be something to look into, because it sounds like your case is quite severe with all extremities affected. Man, that's got to hurt!

Its good that you have been tested for other auto-immune diseases because it is quite common in lupus and scleroderma.

I have found that drinking too much coffee and/or getting dehydrated both make it more likely to come on, so maybe try keeping a check on those things to see if it improves.

With love, Erika